Troops from the 1st Marine expeditionary force, backed up by Iraqi security forces, ordered an 8pm to 6am curfew on Sunday in and around the city, 110km west of Baghdad, as part of what has been dubbed Operation River Blitz.
"The operation is designed to target insurgents and terrorists who have attempted to destabilise the Anbar province by terrorising the populace through wanton acts of violence and intimidation," the US military said in a statement.
"We were asked by the Iraqi government to increase our security operations in the city to locate, isolate and defeat anti-Iraqi forces and terrorists," Marines Major-General Richard Natonski said in the statement.
The US military camp in the city is the target of mortar fire almost daily since the March 2003 war by groups opposed to the foreign military presence.
Iraqi security forces have killed or captured three men producing websites showing captives being tortured, officials said on Sunday, as Indonesia stepped up efforts to try to free two of its journalists kidnapped in Iraq.
The interim government said security forces had "killed the terrorist Adil Mujtaba, known as Abu Rim, who disseminated propaganda for Abu Musab al-Zarqawi's terrorist network".
US and Iraqi forces have stepped
up security operations in Ramadi
Mujtaba was the third al-Zarqawi propaganda chief to be killed or detained after the first and second in command, Abu Sufiyan and Husam Abd Allah Muhsin al-Dulaymi, were respectively killed and detained, a statement said, without providing further details on the latter two.
"Abu Rim [Mujtaba] specialised in creating terrorist websites which encouraged terrorism," it said, adding that he was killed in a raid on 11 February.
"He glorified the murder of innocent people and published images which included terrorists torturing hostages."
Al-Zarqawi, who has a $25-million bounty on his head, is believed to be behind a string of deadly attacks and kidnappings and is the frontman in Iraq for Usama bin Ladin's al-Qaida network.
Six more Iraqis have been killed in separate incidents in Iraq, police and US military said on Sunday, after some 70 others died during the two-day Shia Ashura religious festival which ended on Saturday.
A US marine was killed in action in Anbar province during a military operation west of the capital, the US command said on Sunday.
Some 70 Iraqis died during two
days of the Shia Ashura festival
In the northern city of Mosul, Iraqi security forces killed an anti-interim government fighter after their patrol came under attack, the US military said, adding that US forces had killed a taxi driver in Tal Afar, west of Mosul, after he failed to stop.
In the Saturday shooting, the troops were trying to disable the taxi but ended up killing the driver. His son, who was in the car, was taken home, the military said.
Southeast of Mosul, in Kirkuk, one Iraqi was killed by a car bomb and two more in an apparently accidental blast, police said.
"A car bomb exploded on a provincial road near Hawija and the driver of the car was killed," Kirkuk police chief, General Turhan Yusuf, said, adding that there were no US soldiers or Iraqi patrols in the area, west of Kirkuk, at the time.
In Kirkuk, two Kurds were killed in the apparently accidental explosion of an ammunition dump dating back to before the US-led invasion, Yusuf said.
East of Baquba, some 65km northeast of Baghdad, fighters ambushed and killed an Iraqi soldier as he went home, an army officer said.
In the southern city of Basra, two civilians were wounded when a bomb exploded as an Iraqi police patrol passed, a police spokesman said.
Clashes between anti-US fighters
and US troops continue in Mosul
The patrol pursued a suspect who filmed the attack and detained him after he hid in a tree nursery where they found ammunition and explosives, he said.
Mosul's main medicine warehouse burnt down after catching fire during a clash between anti-US fighters and US troops who were attacked in the city centre, said the man in charge of the building's security.
Also on Sunday, the bodies of three Iraqi soldiers were discovered on a country road west of Baghdad outside Falluja and transported to a hospital in nearby Ramadi where doctors said they had died of bullet wounds.
Residents of Falluja said the town was sealed off by soldiers
after fighters launched a missile at a roadblock operated by US and Iraqi soldiers.
Several military vehicles were set ablaze, but residents said they were unable to determine whether there were casualties.
Also on Sunday, Ukrainian television TV 5 Kanal reported that Ukrainian peacekeepers were preparing to leave Iraq.
Meanwhile, Time magazine has cited Pentagon and other sources as saying that US diplomats and intelligence officers were conducting secret talks with "Sunni insurgents" on ways to end the fighting.
The Bush administration has said it will not negotiate with Iraqi fighters and there is no authorised dialogue, but the US is having "back-channel" communications with certain fighters, unidentified Washington and Iraqi sources told the magazine.
The White House had no immediate comment on Sunday's report.
US senators have voiced concern
over Ibrahim Jafari's Iran links
In other developments, visiting US Senator Hillary Clinton said there were grounds for concern if Iraqi interim Vice-President Ibrahim al-Jafari was picked as Iraq's new prime minister, pointing to his ties to neighbouring Iran.
Clinton was interviewed from Iraq alongside Republican Senator John McCain, who said al-Jafari appeared likely to become the next premier.
"I think we know that he is probably going to be the prime minister," McCain told NBC's Meet the Press.
Clinton, a New York Democrat and former first lady, said: "There are grounds both for concern and for ... vigilance about this."
She added: "It is a historical fact that he along with the Dawa party have had connections with Iran," partly because of their common opposition to former Iraqi leader Saddam Hussein.