BAGHDAD -- Residents started to trickle back to the besieged city of Fallujah on Friday as militants and government forces both appear to be preparing for a long standoff. Al Qaeda-linked fighters and tribal gunmen are camped on the outskirts of the city, with Iraqi army and police stationed nearby.

A tense calm has settled over the city, although sporadic street fighting rattled Ramadi and surrounding areas in Sunni-dominated Anbar province, a vast desert region west of Baghdad that was once a major battleground for U.S. troops.

The extremist militants, emboldened by fellow fighters' gains in the civil war in neighbouring Syria, have tried to position themselves as the champions of Iraqi Sunnis angry at the Shiite-led government over what they see as efforts to marginalize them.

Violence spiked after the Dec. 28 arrest of a Sunni lawmaker sought on terrorism charges and the government's dismantling of a year-old Sunni protest camp in Ramadi, the provincial capital, and Iraqi police were forced to retreat from the city centres as black masked gunmen overtook Fallujah and parts of Ramadi last week, burning down police stations and posting guards outside strategic areas.

Iraqi troops have taken up positions in and around both cities but have not launched major urban offensives, fearing that likely civilian casualties could incite Sunni anger and push moderate tribal leaders to side with the extremists.

Defence Ministry spokesman Mohammed al-Askari told The Associated Press on Friday that the government's patience would not last forever.

"If there is no other solution, then the security forces and allied tribal fighters will enter these cities," al-Askari said.

Clashes broke out again Friday, this time between Iraqi special forces and militants in the village of al-Bubali, between Fallujah and Ramadi. Roadside bombs planted around the village damaged several army vehicles, a police officer said, speaking on condition of anonymity because he was not authorized to talk to the media. There was no immediate word on casualties.

Central areas of Fallujah, about 65 kilometres west of Baghdad, have been calm in recent days, according to accounts from residents and international observers.

That could be an indication that at least some al Qaeda fighters heeded a call by influential tribal leaders earlier in the week to pull out of town or face confrontations not only with the army but also with fellow armed Sunnis who want the outsiders gone.

Many of the al Qaeda fighters and some armed local tribesmen who want to keep government forces out are now stationed in largely unpopulated areas on the outskirts of Fallujah, overlooking approaches to the city from the main highway that connects Baghdad with Syria and Jordan.

But other anti-government gunmen, their faces hidden by scarves, remain on the streets of the city in an intimidating show of force meant to prevent Iraqi forces from militarily retaking the city and deter would-be bank robbers and other looters.

Some residents have started to return to Fallujah, often only briefly to check that their houses are safe. Markets have begun to reopen as well, restoring some sense of normalcy to the city.

But the situation remains tense, with many police stations abandoned after they were torched by militants and health care facilities running short on supplies.

"The government services and medical situation in Fallujah is very bad because of the absence of civil servants and policemen. The tribal gunmen are in control of the city," said Dhari al-Arsan, deputy governor of Anbar, who lives in Fallujah.

International observers have warned of shortages of food, fuel and other necessities, particularly in Fallujah. United Nations records show that more than 11,000 families have been uprooted by the fighting throughout Anbar.

The UN envoy to Iraq, Nickolay Mladenov, described the situation in Fallujah as "very, very fluid" and said the city remains under the control of various armed groups.

"Restoring order to Fallujah, pushing the terrorist elements out of the cities, delivering humanitarian aid: these would be the immediate priorities," he said in an interview.

He praised the level of co-operation at both the national and local level in finding a way out of the crisis.

"The UN is getting very good co-operation with the government, the local authorities and the tribes," he said.

Pawel Krzysiek, a Baghdad-based spokesman for the International Committee of the Red Cross, said the "humanitarian situation is still dire" in Fallujah, though not as dramatically so as during the peak of the fighting. The Red Cross has managed to deliver some emergency supplies in Anbar but needs greater access from all sides to ensure aid gets through, he said.

Determining exactly who all the gunmen are and where their loyalties lie remains a challenge. It is in many ways a parallel to the various factions of Sunni fighters among the rebels fighting to topple Syrian President Bashar Assad.

In addition to the al Qaeda fighters who overran Fallujah and Ramadi last week, many of whom do not hail from the cities, local anti-government tribesmen have taken up arms. Some but perhaps not all claim to oppose al Qaeda's extremist ideology.

Other armed tribesman are firmly opposed to al Qaeda's presence in the area. Among them are members of the Sahwa, a government-supported militia that joined the U.S.-led fight against al-Qaida insurgents during in the years following the 2003 invasion and is widely credited with helping beat back al-Qaida in the past. In many cases, those tribesmen may have family links with the anti-government local militiamen and for now appear to be avoiding clashing with them.

"The situation is so complicated because you've got the tribal groups who are allied with the government ... and other groups ... against the government who are fighting Iraqi government forces and al Qaeda," said Erin Evers, a Mideast researcher for Human Rights Watch, which has been monitoring the fighting by speaking with residents in the affected areas. "We don't have a clear enough picture or even clear casualty figures. People who are ending up in the hospital, we don't know who killed them."

Sheik Ahmed Abu Risha, a powerful Anbar tribal leader who heads the Sahwa, told the AP on Friday that he believes he has enough fighters and weapons, some supplied by the Iraqi army, to confront the al Qaeda militants.

He alleged that some of the militants have been using civilians as human shields, making his men reluctant to try to confront them head-on because of concerns about civilian casualties.

The situation in Ramadi remains more volatile. Burned-out armoured vehicles and police cars line the highway where an anti-government protest camp stood until it was demolished by government forces in late December.

Scattered clashes continue to erupt in different parts of the city, including a number of gunbattles that broke out late Thursday and again on Friday, according to local and international officials. The risk of violence has persuaded residents to shelter indoors at night.

"Ramadi turns into a ghost town after sunset," al-Arsan said.

Schreck reported from Dubai, United Arab Emirates. Associated Press writer Sameer N. Yacoub contributed reporting from Baghdad.