Iraqi Prime Minister Nouri Maliki has asked for construction to end on a concrete wall around a Sunni enclave in the capital, Baghdad.
US troops are building the wall at night under tight security
Mr Maliki said there were other ways to protect the Adhamiya neighbourhood, which is surrounded by Shia districts.
The US military, which is behind the project, has said the purpose of the wall is to prevent violence between Sunni and Shia militants.
But Iraqi politicians have warned it will increase sectarian tensions.
Speaking in Cairo after meeting Arab league officials, Mr Maliki said: "I asked yesterday that it be stopped and that alternatives be found to protect the area."
The prime minister said he feared the wall may have unintended consequences, in an apparent parallel to the former Berlin Wall that divided the German capital.
"I fear this wall might have repercussions which remind us of other walls, which we reject," he said.
Construction of the 5km (3-mile) concrete wall began on 10 April and the US military says it hopes to complete the project by the end of the month.
US troops, protected by heavily-armed vehicles, have been working at night to build the 3.6m (12ft) wall.
Earlier this week, senior Sunni politician Adnan al-Dulaimi, who heads the largest Sunni bloc in parliament, said the barrier would breed yet more sectarian strife.
Residents also said the wall would do little to improve bitter relations between the communities.
US and Iraqi troops have long built cement barriers around key locations in Baghdad and other cities to prevent attacks, especially suicide car bombings.
Iraq has been in the grip of raging sectarian violence since the bombing of an important Shia shrine in Samarra in February 2006.
US forces in Iraq have said they would respond to issues surrounding the barrier on Monday.