Kenya's border with Somalia will re-open in April almost 15 years after it shut because of attacks by Islamist militant group al-Shabab, President William Ruto has announced.

Based in Somalia, the group has masterminded a series of deadly assaults in Kenya including one on a shopping centre in the capital, Nairobi, killing 67 people in 2013 and one at a university in Garissa two years later killing 148.

The plan has been announced before, in 2023, but further attacks postponed the arrangements.

Ruto said the intention to re-open two crossings follows years of security assessments, adding that there will be a heavy deployment of security forces to ensure the move does not compromise safety.

Kenya has also been concerned about illicit weapons and other contraband goods being smuggled across the border.

The border was closed in October 2011, when the East African nation launched a major military incursion into Somalia to push back al-Shabab - an al-Qaeda affiliate - from its border.

These soldiers were later absorbed into the African Union force, a version of which is still in Somalia and still has a Kenyan contingent.

Ruto's announcement came days after the Mogadishu-based Hiraal Institute think-tank issued a wide-ranging report about the security situation in Somalia, saying that al-Shabab was growing in strength and had regained most of the territory in central areas it lost in a big government offensive in 2022.

"The pattern of al-Shabab's territorial recovery reveals both the group's strategic acumen and the government's structural weaknesses," the report said.

The government's offensive had been hasty - taking advantage of an uprising over taxes imposed by the militants - but it did not have a strategy to reclaim its sovereignty fully, according to Hiraan's Mohamed Mubarak.

"The nature of the operation caused a huge desertion of forces," he told the BBC's Newsday programme.

"With the government's mandate ending in less than three months… I don't think there's going to be any more operations against al-Shabab in the foreseeable future."

President Ruto announced the plan to reopen the frontier on a visit to the border town of Mandera, in Kenya's far north-east, which has a large population of ethnic Somalis.

"It is unacceptable that fellow Kenyans in Mandera remain cut off from their kin and neighbours in Somalia due to the prolonged closure of the Mandera Border Post," Ruto posted on X.

He hoped that the re-opening would boost "cross-border trade for the mutual prosperity of our people".

In a speech, he asked all residents of Mandera, which has been targeted several times, to "join in the battle against al-Shabab. These al-Shabab are useless, I want to assure that Kenya will work together with you, just help us combat these criminals and terrorists."

In addition to the attack on the Westgate mall and Garissa University, other major al-Shabab attacks in Kenya include the killing of 28 bus passengers in Mandera county in 2014 and an assault on a hotel in Nairobi five years later which left at least 21 people dead.

In 2015, Kenya had embarked on building a perimeter barrier along the countries' 680km (423-mile) common border because of the militant threat but the project was suspended after nearly three years when only 10km (six miles) of a wire fence had been built at a cost of $35m (£26m).