Mercedes Aráoz said the “constitutional order had broken” and that the country faced a “grave institutional crisis”.
President Martín Vizcarra on Monday dissolved Congress, but opposition MPs suspended him and swore in Ms Aráoz.
On Tuesday, armed police blocked legislators from entering Congress.
Some 20 MPs were inside the congressional building in the capital, Lima, refusing to leave in protest against President Vizcarra’s dissolution, while streets around parliament were in lockdown.
In a late-night post on Twitter, Ms Aráoz cited a statement by the Organization of American States that Peru’s constitutional court should determine the legality of Mr Vizcarra’s decision to dissolve Congress.
She said she hoped that her resignation would lead to a general elections being called as soon as possible, for “the good of the country”.
What happened on Monday?
Mr Vizcarra dissolved Congress, saying opposition legislators had blocked him from passing a raft of anti-corruption measures. He argued that his move was constitutional, but opposition parliamentarians said it was dictatorial and have refused to leave the building.
A majority of the opposition-controlled Congress then voted in favour of suspending Mr Vizcarra for a year, and declared Ms Aráoz acting president. But the government claimed the moves were null and void because they had occurred after Congress had been dissolved.
The stand-off is likely to continue over the coming days, with Congress planning to meet again on Friday to vote on a motion to dismiss the president altogether.
Mr Vizcarra – who seems to have the support of the armed forces and the police – has issued a decree setting parliamentary elections for 26 January. Meanwhile, a legal battle is expected to kick off to determine if the dissolution of Congress was constitutional or not.
How did it come to this?
Mr Vizcarra was sworn in in March 2018 after his running mate and then-President Pedro Pablo Kuczynski resigned over a vote-buying scandal.
He said he would fight corruption head-on, which endeared him to Peruvians tired of endless scandals that have tainted not only Mr Kuczynski but also the three previous presidents.
Peru’s scandal-tainted presidents
- Pedro Pablo Kuczynski: Under house arrest while under investigation for alleged corruption linked to Brazilian construction giant Odebrecht
- Ollanta Humala: Accused of accepting $3m in illegal financing from Odebrecht for his electoral campaign
- Alan García: Killed himself in April as police arrived to detain him over bribery allegations also linked to Odebrecht
- Alejandro Toledo: In jail in the US, Peru has requested his extradition for allegedly taking $20m in bribes from Odebrecht
Mr Vizcarra says Congress, dominated by the right-wing Popular Force party led by Keiko Fujimori, blocked his measures, and accused the party of trying to shield itself from corruption investigations by obstructing the reforms.
Ms Fujimori, the daughter of former President Alberto Fujimori, is in jail awaiting trial for allegedly accepting illegal funds from Odebrecht.
The president also argued that Congress’s appointment of a new judge to the constitutional court would interfere with his efforts to stamp out corruption. Among other things, the court is soon due to decide whether to free Keiko Fujimori from pre-trial detention.