Armenian Prime Minister Serzh Sargsyan has resigned after days of large-scale street protests against him.
Opposition supporters accused Mr Sargsyan of clinging to power after he was appointed prime minister last Tuesday, soon after finishing two five-year terms as president.
“The street movement is against my tenure. I am fulfilling your demand,” he said in a statement.
Former prime minister Karen Karapetyan takes over as acting PM, reports said.
The announcement came soon after opposition leader Nikol Pashinyan was released from detention. Mr Pashinyan had been arrested on Sunday after televised talks with Mr Sargsyan collapsed.
As well as Mr Pashinyan, two other opposition politicians and some 200 demonstrators were held.
In his statement published on his website, Mr Sargsyan said he was “addressing all citizens of the Republic of Armenia… for the last time as leader of the country.”
“Nikol Pashinyan was right. I was wrong,” he said. “The situation has several solutions, but I will not take any of them… I am leaving office of the country’s leader, of prime minister.”
His spokesman, Hovhannes Nikoghosyan, told the BBC that Mr Sargsyan was behaving responsibly and fulfilling the demands of the street movement which opposed his appointment as prime minister.
“I think his resignation is a clear demonstration of a democracy in force. It’s not that every demonstration in every corner of the world leads to the resignation of the authorities,” Mr Nikoghosyan said.
Protesters chanted “Nikol, Nikol” in the streets on Monday and waved Armenian flags. They were joined by hundreds of uniformed soldiers, despite warnings from the defence ministry that any soldiers protesting would be harshly punished.
Mr Pashinyan congratulated the people on their “victory” following the resignation. “You have won, proud citizens of the Republic of Armenia. And no one can seize this victory from you. I congratulate you, victorious people,” he wrote on Facebook.
Mr Sargsyan had faced criticism in Armenia over his close ties to the Russian President, Vladimir Putin, who has also moved between roles as president and prime minister to maintain his grip on power.
Mr Putin’s spokesman said on Monday that Moscow was closely watching events in Yerevan. “We are very attentively observing what is happening in Armenia,” Dmitry Peskov told journalists, calling the country “extremely important” for Russia.
Asked if Russia would intervene, Mr Peskov said the matter was “exclusively an internal affair” and Russian action would be “absolutely inappropriate”.
Why were there protests?
In 2015, Armenians voted in a referendum to shift the country from a presidential to a parliamentary system, stripping powers from the president and giving them to the prime minister.
The vote was marred by allegations of ballot rigging and claims Mr Sargsyan wanted to simply switch office after his presidency ended.
The ex-president had formally stated he would “not aspire” to the prime ministerial position, but on Tuesday last week the country’s parliament officially confirmed Mr Sargsyan in the post.
Protesters poured into the streets in the days beforehand to try to stop the parliament from passing the measure, and clashed with police. On the day of the confirmation, Mr Pashinyan said the demonstrations constituted a “non-violent velvet revolution”.