A Shiite militia group in Iraq said it was responsible for a deadly attack earlier this week that killed five American troops.
The Iranian-backed Kataib Hezbollah posted the claim on its website late Thursday. The U.S. military announced the deaths of the five American soldiers Monday, the single largest loss of life for American troops in two years. It said its base was hit by indirect fire, a military term for rockets and mortars.
Kataib Hezbollah, which has links to the Lebanon-based Hezbollah group, is one of three main Shiite militias operating in Iraq.
All staunchly oppose the U.S. military presence in Iraq and have vowed to oppose any move for U.S. troops to stay past their expected Dec. 31 departure date.
Kataib Hezbollah said it would continue to target American military bases.
In Washington on Thursday, Leon Panetta, the likely next Defense Department chief, predicted that Iraq will ask the United States to maintain a presence there beyond the end of this year, when U.S. troops are scheduled to leave.
About 47,000 U.S. troops remain in Iraq, none in a declared combat role. They are slated to leave under an agreement reached in 2008 shortly before President Barack Obama entered the White House.
Also Friday, about a thousand protesters returned to Baghdad's Tahrir Square.
Many protesters there and in other cities around the country opposed Prime Minister Nouri al-Maliki's decision to not fire anyone in his Cabinet after this week's expiration of a self-imposed 100-day deadline for reforms. Al-Maliki had promised to purge his government of corruption and dysfunction and provide more electricity and better public services, but the deadline passed earlier this week with little fallout.
Six weeks of protests swept across Iraq earlier this year, some of which turned deadly. None of the demonstrations reached the fervor of the uprisings that toppled governments in Egypt and Tunisia.
In Baghdad, most of Friday's demonstrators were actually pro-government, in an apparent attempt to overshadow any anti-government sentiment. The pro-government protesters were demanding the execution of an alleged al-Qaida member detained recently on charges of being behind several attacks, including the massacre of 70 people at a wedding party in 2006.
Government figures including the human rights minister attended the protest.