Four opposition figures have been arrested in Nicaragua in what government critics have called a hunt for critics of President Daniel Ortega.

Two of those detained on Tuesday are potential candidates in the election in November, in which Mr Ortega is expected to run for a fifth term.

Their arrests bring the total of presidential hopefuls in detention to four.

The US branded Mr Ortega "a dictator" following Tuesday's arrests.

Who's been detained?

In a space of 12 hours on Tuesday, the following opposition figures were arrested:

Félix Maradiaga, academic and political activist who was planning to run as an opposition candidate in the presidential election
Juan Sebastián Chamorro, economist and presidential hopeful
José Adán Aguerri, economist and head of the Committee on Economic Integration
Violeta Granera, sociologist and opposition activist

Two more presidential hopefuls - former ambassador Arturo Cruz and Cristiana Chamorro - were detained in the past week.

Ms Chamorro was charged with money laundering days after announcing that she would seek to become the presidential candidate for the opposition Citizen's Alliance.

She is seen by many in the opposition as their best hope of defeating Mr Ortega at the ballot box. Her mother Violeta Chamorro beat him in the 1990 presidential poll.

Ms Chamorro and Ms Granera are under house arrest, while Mr Chamorro and Mr Aguerri are in police detention.

A lawyer for Mr Maradiaga said his client was being held at an undisclosed location and had been badly beaten as he was taken into custody.
What are they accused of?

All of those detained, except for Cristiana Chamorro, have been accused of plotting against Nicaragua's sovereignty and independence and of organising terrorist acts with financial help from foreign powers.

They have been detained under a controversial treason law passed in December by Nicaragua's National Assembly, which is dominated by government allies.
What is the treason law?

Under the law, the government has the power to ban candidates from running for office if they are deemed to be traitors to Nicaragua. Anyone designated a traitor can be sent to prison for up to 15 years.

The government says the law aims to protect "the independence, the sovereignty and self-determination" of Nicaragua. It says the country is under threat from imperialist powers in the US and "coup-mongers" within Nicaragua who are determined to overthrow President Ortega.

But critics say the law is designed to stop opposition politicians from standing in the election.
What reaction has there been?

Tweeting after Mr Maradiaga's arrest, the top US diplomat for Latin America, Julie Chung, said the move "should resolve any remaining doubts about Ortega's credentials as a dictator".

José Miguel Vivanco, the Americas director for Human Rights Watch, also took to Twitter, saying: "In the last 30 years, I've never seen anything like it. Multilateral efforts are urgently needed to stop Ortega."

Ms Chamorro's brother, Carlos Fernando Chamorro, told the BBC that Daniel Ortega was removing anyone who might challenge him. "This is just an attack against basic rights of political competition. In the past he had several hundreds of political prisoners as hostages. Now he has captured four aspiring presidential candidates as hostages."

Shortly before being led away by police, Mr Maradiaga said he would not give up fighting. "What we have done is fight alongside the Nicaraguan people, and we will continue to do so," he said.

Mr Chamorro vowed to resist in a video he recorded before being summoned by the authorities: "This is a good fight, for good causes. Let's not let a criminal dictatorship take away our rights any longer.".
Who is Daniel Ortega?

President Ortega, 75, is expected to seek a fourth consecutive term in November's election. But opinion polls suggest his popularity has plummeted after the violent crackdown on anti-government protests in 2018 in which hundreds of people were killed.

The United States, the UK and the EU have imposed sanctions on Nicaraguan officials, whom they accuse of undermining democracy.

First took power in 1979 as the head of the leftist Sandinista rebel movement, ousting dictator Anastasio Somoza
Defeated in 1990 election by Violeta Chamorro after economic failures resulting from US sanctions and war against US-backed right-wing rebel groups known as Contras - then loses two more elections
Accused of sexual abuse by own stepdaughter in 1998
Re-elected in 2006 after rebranding as Christian socialist
Allowed to stand for re-election in 2011 and 2016 following constitutional changes, and re-elected
Resisted calls to step down after violent suppression of uprising in 2018

From revolutionary leader to opposition hate figure