The political followers of Iraq's radical Shia cleric, Moqtada Sadr, say they are ending a two-month boycott of Iraq's parliament and government.
The Sadr alliance say their grievances have been addressed
The boycott was imposed as a protest over a planned meeting between Iraq's prime minister and President Bush.
Correspondents say the move signifies an easing of tensions among Shia groups in Iraq's government.
The anti-US group, a key member of PM Nouri Maliki's coalition, has 32 MPs in the 275-seat parliament.
The Mehdi Army, the Shia militia loyal to Moqtada Sadr, has fought sporadic battles with the US since 2003 and has been identified as a disruptive force within Iraq by Washington.
The Sadrists announced their decision at a news conference with senior figures from the umbrella Shia alliance.
"Since there has been a response to our demands, we declare that we will attend parliament today," said Bahaa al-Araji, a Sadrist spokesman.
Opposition to the continued US presence in Iraq has been a key feature of the group's demands.
At the news conference, parliamentary speaker Mahmoud al-Mashadani said all parliamentary parties would now form a committee to discuss the reasons for the boycott and resolve the issues.
"This is a new beginning," he said.
"We want to say to the world that an Iraqi solution for Iraqi problems is the key, and others must support these solutions."