By Dean Yates and Ibon Villelabeitia

BAGHDAD (Reuters) - Iraq's prime minister said on Sunday he had urged the U.S. military to halt work on a wall separating a Baghdad Sunni enclave from nearby Shi'ite areas after sharp criticism from some residents.

The cement wall around the district of Adhamiya is part of a new U.S. military tactic to protect flashpoint neighborhoods with barriers, in a security crackdown in the capital that is seen as a final attempt to halt civil war between majority Shi'ites and minority Sunni Arabs.

Car bombs killed 18 people in Baghdad on Sunday and gunmen shot dead 23 workers from an ancient minority sect after pulling them off a minibus in the northern city of Mosul in an apparent revenge attack.

Speaking in Cairo at the start of an Arab tour to drum up support for Iraq, Prime Minister Nuri al-Maliki, a Shi'ite Islamist, said he objected to the 5-km (3-mile) wall, which residents said would isolate them from other communities and sharpen sectarian tensions.

"I asked yesterday that it be stopped and that alternatives be found to protect the area," Maliki said in his first public comments on the issue.

"I said that I fear this wall might have repercussions which remind us of other walls, which we reject," he added.

Some Adhamiya residents have compared the wall to barriers erected by Israel in the occupied West Bank.

The U.S. military sought on Sunday to play down any hint of friction between Maliki and American commanders behind the Baghdad plan, saying it would coordinate with the Iraqi government and Iraqi commanders on how best to establish security measures.

"The government of Iraq and MNF-I (Multinational Force-Iraq) do agree that we need to protect the people of Iraq. How that is done is always being discussed and we will continue that dialogue," the military said in a statement.

Among Sunday's attacks in Baghdad, two suicide car bombers rammed their vehicles into a police station in a mostly Shi'ite neighborhood, killing 12 people and wounding 95, police said.

It was one of the deadliest bombings aimed at Iraq's security forces since the crackdown was launched two months ago.

"Look at the situation Iraqis are living in. You see blasts whenever you try to go out to earn a living," said one witness.

ANCIENT SECT

In Mosul, gunmen killed 23 textile workers from the minority Yazidi sect after forcing them out of a minibus.

Brigadier-General Mohammed al-Waggaa said the gunmen stopped the vehicle and gunned down the workers.

Waggaa said the mass killing appeared to be in retaliation for an incident in which a Yazidi woman was stoned to death several weeks ago for converting to Islam. Another police source who declined to be named confirmed the incident.

U.S. and Iraqi forces have poured thousands of extra troops into Baghdad over the past two months.

While the boost in troop levels has reduced killings by sectarian death squads, car bomb attacks still plague the city. A wave of car bombs killed nearly 200 people last Wednesday.

U.S. Defense Secretary Robert Gates told Iraq's leaders on Friday that progress in reconciling warring Shi'ites and Sunni Arabs would be an "important element" when Washington decides this summer whether to maintain the higher troop numbers.

But remarks by senior U.S. commanders and officials and a change in Army deployment plans suggest the higher level of American troops will likely remain for months beyond the summer.

Washington has avoided saying how long it will keep the beefed-up force of about 160,000 troops ordered in January.

It has said only that it will review progress in the late summer. The implication is that troops could then start to be withdrawn but that appears improbable.

The U.S. military commander in Iraq, General David Petraeus, said during Gates' visit that the buildup of some 28,000 extra U.S. troops would not even be complete for another two months.

(Additional reporting by Yara Bayoumy, Wissam Mohammed and Ahmed Rasheed, Andrew Gray in Washington and Mohamed Abdellah in Cairo)