Toting sub-machine guns and sometimes wearing masks as they drive along the streets of Uganda, members of an elite military unit are increasingly viewed as a private army to keep 81-year-old President Yoweri Museveni in power - along with his ever-growing family dynasty.

Museveni has led Uganda since 1986, when his rebel forces marched into the capital, Kampala. He has since won four elections - all marred by allegations of violence and rigging.

But this is nothing new in the country - since Uganda gained independence in 1962, power has only ever changed hands through rebellions or military coups.

Museveni is seeking re-election next year and the opposition fears that the Special Forces Command (SFC) could be used to prevent it from campaigning, as it says was the case in 2021.

But the SFC, which for years was commanded by Museveni's son Gen Muhoozi Kainerugaba, has been accused by government critics of abducting, torturing and killing opposition activists all year round, not just during elections. The SFC denies these allegations.

"It's like a shadow army within the army which is only answerable to the president and his son. Its rise and influence is causing resentment among senior generals," one military source told the BBC.

This is compounded by the fact that Gen Kainerugaba, 51, who is now the army chief, and has said he wants to succeed his father one day, has enlisted his own son into the army.

Gen Kainerugaba has also been contemptuous of some long-serving generals, calling one a "buffoon".

His remarks sent shockwaves through military and political circles, but the government downplayed them as "mere social-media banter" - something for which Gen Kainerugaba is well known.

Several years ago he made a joke remark about invading neighbouring Kenya, to the dismay of generals.

Analysts say the unit has become so influential that it rivals the power of the regular army, which still has commanders who fought in the guerrilla war that brought Museveni and his National Resistance Movement (NRM) to power.

These observers have raised fears that the two could clash one day - as in Sudan where a civil war has broken out following a power struggle between the army and a paramilitary group once allied with it, the Rapid Support Forces (RSF).

The unit now known as the SFC was established when Museveni first took office, and has a motto stating "there is no substitute for loyalty".

"The SFC is the most powerful unit within the Ugandan military, comprising the [most] highly trained, best-equipped, and best-funded officers in the country," Dr Gerald Bareebe, a Uganda-born academic based at Canada's York University, told the BBC.

Both the Ugandan army and the SFC declined to comment when approached by the BBC.

Museveni has previously defended the SFC, saying it was formed for Ugandans. He said that only people who did not wish Uganda well could be unhappy with such a force.

But Museveni's critics see it differently - arguing that the president has ruled with an iron fist since seizing power, and has turned the country into his family's fiefdom.

They note that the president's wife, Janet, is the education minister and Gen Kainerugaba is the army chief. His grandson's enrolment into the army - announced in July - is seen as perpetuating the family dynasty.

Gen Kainerugaba has twice led the SFC and is credited with expanding it into a force with an estimated membership of more than 10,000. The regular army is thought to have around 40,000 active members.

"They go through specialised training. And also they have sophisticated weapons, unlike the regular army," a former senior military officer told the BBC.

Although his father promoted him to chief of the defence forces in March last year, Gen Kainerugaba is said to have maintained de facto control over the SFC, with its current commander, Maj Gen David Mugisha, reporting to him.

Gen Kainerugaba mostly operates from the unit's headquarters - in a building named after his father - in Entebbe, about 34km (21 miles) south of the capital, Kampala.

The SFC boasts on its website that it carries out specialised missions "at a moment's notice", and is assigned to secure critical installations such as the main airport and oil fields.

It is widely suspected to have crossed into Kenya last November to capture opposition politician Kizza Besigye, once Museveni's doctor, and take him back to Uganda to face trial for treason, which has yet to start. The army's prosecutor has acknowledged the involvement of the Ugandan security forces.

Analysts like Dr Bareebe feel the SFC's core function "is to guarantee regime survival" by fending off threats - not only from the opposition but also army generals.

"It plays a disproportionately central role in suppressing anti-regime mobilisation and shielding the ruling NRM from both internal dissent and external threats," Dr Bareebe said.

Although the SFC has denied involvement in the wave of abductions and torture of opposition members, some of its officers have been convicted of abusing their power.

The most prominent case was that of a 32-year-old SFC soldier, who was court-martialled and sentenced to death last November for shooting dead three people and injuring two others, including a one-year-old child.

In May, the presidency said it was investigating a reported incident where SFC soldiers were accused of torturing the driver of a boda boda - as motorbike taxis are known locally. The rider had been rushing to reach his pregnant wife when he got caught up in a presidential convoy.

In the same month, Gen Kainerugaba sparked public outrage after he confirmed the detention of an opposition leader's bodyguard, who had been missing for days.

He said his "boys" were holding Edward Sebuufu, alias Eddie Mutwe, "in my basement", and in a social media post, attached a photograph of the bodyguard with a clean-shaven head.

Gen Kainerugaba mocked Mr Sebuufu, saying he was "looking very smart these days" as his beard had been shaved by "my boy", referring to a junior soldier.

The Uganda Law Society said Mr Sebuufu's ordeal had not been an isolated case, but was "part of a systematic campaign to silence dissent and crush the aspirations of people yearning for freedom".

It added that the incident underscored "a dangerous nexus of military power and political oppression".

The shadowy nature of the unit and its operations have often led to accusations that its existence was illegal.

But in June, parliament passed a controversial legislative amendment, recognising the SFC as one of four official military services - along with the land forces, air force and reserve force.

Opposition MPs criticised the move, saying the unit should not be given such legitimacy and should instead be disbanded.

"The new law validates an entity that has been operating illegally," said opposition MP Ibrahim Ssemujju Nganda.

For Dr Bareebe, the SFC's "elevation in law merely reflects its already dominant position within Uganda's militarised power structure and reinforces its role as the cornerstone of regime security".

This concern was shared by respected Ugandan analyst Godber Tumushabe. He recently warned that despite the country's apparent stability, "all that we have is the absence of war".

A senior army officer, who preferred not to be named for fear of repercussions, told the BBC that there has been growing discontent within the military about the unit's recruitment process as it appeared to be along ethnic lines.

Various sources, including those in the military, told the BBC that the SFC was heavily dominated by officers from President Museveni's Banyankore ethnic group, and related communities, in order to guarantee loyalty.

"If you look at all SFC commanders since its inception, they come from Museveni's ethnic group," says Nganda, the opposition MP.

Of the six commanders who have held the position since 2007, only one does not hail from the west country, where the Banyankore live.

Given these competing interests, analysts fear that a power struggle could break out between rival military factions in the post-Museveni era.

"My greatest fear is that we don't know what will happen when Museveni goes and there is dissent within the army," Nganda said.

Dr Bareebe echoed this concern: "A stand-off between the SFC and the regular army - each with its own loyalties, interests, and command structures - could trigger significant political instability and even violence, especially in the absence of a clear succession plan."

But other analysts disagree, saying that this is where Gen Kainerugaba will come into his own given his long career with both the army and SFC.

They argue he is well placed to hold the rival factions together and ensure that the Museveni dynasty continues, guaranteeing stability in Uganda.

Such an outcome would of course be seen as undemocratic by the opposition.

Robert Kyagulanyi, a former pop star better known as Bobi Wine who is running against President Museveni for a second time next year, describes the unit as a "torture squad".

Earlier this year Gen Kainerugaba threatened to behead the opposition leader, though he later deleted the "joke" tweet and apologised.

Bobi Wine told the BBC he and his colleagues were often targeted and beaten up by SFC officers - and he wants the squad disbanded.

"This is largely seen as the section in the military that is responsible for regime survival through brutality," he said. "They operate with impunity and they operate under the protection of General Museveni and his son."