Tunisia's interim government has legalised Ennahda, the moderate Islamist group banned under former President Zine al-Abidine Ben Ali.
The move paves the way for Ennahda to form a political party to stand in elections expected later this year.
Meanwhile, two more ministers have quit the government - meaning five senior figures have walked out this week.
Rights group Amnesty has called on ministers to investigate deaths during the protests that toppled Mr Ben Ali.
More than 200 people are thought to have been killed during the unrest, and Amnesty says the interim government must hold those responsible to account.
But the interim government, tasked with organising elections and restoring order, continues to be rocked by protests and resignations.
The cabinet's most prominent opposition leader Najib Chebbi resigned on Tuesday, saying he did not agree with the direction of the government.
Another minister also quit, one day after two other ministers walked out.
Prime Minister Mohammed Ghannouchi, who had retained the office he held under Mr Ben Ali, resigned on Sunday in a bid to end street protests.
But the protesters who helped bring down Mr Ben Ali were furious that so many of his former allies were included in the interim government, and continued their protests.
The legalisation of Ennahda was another of the protesters' demands.
The group's 69-year-old leader Rachid Ghannouchi (no relation) arrived back in Tunisia at the end of January after more than 20 years in exile.
He was greeted at the airport by thousands of his supporters, suggesting the group has maintained some of its popularity.
In 1989 Ennahda came second to the ruling party in elections, officially winning about 17% of the ballot in a count widely suspected to favour the ruling party.
The party was banned shortly afterwards, and Mr Ghannouchi fled the country during a crackdown by the Ben Ali regime.
On his return, Mr Ghannouchi told the BBC that his group would not be fielding a candidate for president in the forthcoming election.