Baghdad - Five bicycle bombs and a hail of mortar shells ripped apart a market south of Baghdad on Saturday, killing 18 people in yet another sign that Iraq's government and US forces were struggling to contain sectarian violence. Three US Marines also were killed, making October the deadliest month for American forces this year.

In Washington, US President Bush met with his top military and security advisers to study new tactics to curb the staggering violence in Iraq, where more than 3 1/2 years of war have now taken more American lives, at least 2,791, than the Sept. 11 attack on the World Trade Center.

US officials have blamed the skyrocketing violence on the holy month of Ramadan, which Five bicycle bombs and a hail of mortar shells ripped apart a market south of Baghdad on Saturday, killing 18 people in yet another sign that Iraq's government and US forces were struggling to contain sectarian violenceends Sunday for Sunni Muslims, as well as the increased vulnerability of American forces during a major two-month security sweep in Baghdad and the approaching US midterm election.

A senior US State Department official offered an unusually candid assessment of the security situation in an interview Saturday with Al-Jazeera television, saying the US had shown "arrogance" and "stupidity" in Iraq. Alberto Fernandez, director of public diplomacy in the Bureau of Near Eastern Affairs, also said the US was ready to talk with any Iraqi group except al-Qaida in Iraq to facilitate national reconciliation.

At least 44 Iraqis were killed or found dead Saturday, keeping the month on pace to be the deadliest for Iraqis since April 2005. So far this month, at least 907 Iraqis have been killed in war-related violence, an average of 43 a day.

That compares to an average daily death toll of about 27 since April 2005. The count includes civilians, government officials and police and security forces, and is considered a minimum based on news reporting. The actual number is likely higher, as many killings go unreported.

The United Nations has said at least 100 Iraqis are now killed daily.

The deaths of the Marines raised the October death toll for American troops to 78, surpassing the year's previous high figure of 76 in April. With more than a week left in the month, October is on course to be the deadliest month for American service members in two years.

Despite the grim statistics, a British government minister said Saturday he expects Iraqis to take over much of the work being done by coalition troops within a year.

"The Iraqi army is coming along very well," Foreign Office Minister Kim Howells told British Broadcasting Corp. radio. "I would be very surprised if there was not that kind of capacity taking on a lot of the work done by the coalition forces."

The brutal market attack occurred in the violence-ravaged town of Mahmoudiyah shortly before Muslims began to prepare iftar, their evening meal to break the day's Ramadan fast. It also came two days before the Eid al-Fitr holiday, the day of feasting at the end of the Ramadan month.

A dozen mortars rained down on the market soon after the bombs hidden in plastic bags left on bicycles exploded, said police Lt. Hayder Satar. Such dual attacks are frequently employed by armed groups to inflict additional damage on crowds that form after the initial bombing.

Police said they discovered and disarmed a sixth bomb-laden bicycle, Satar said. He said about 70 people were wounded and taken to hospitals.

Until about a year ago, the town 18 miles south of Baghdad was about evenly mixed between Shiite and Sunni Muslims. Fighters of the Mahdi Army, loyalists of radical Shiite cleric Muqtada al-Sadr, have since moved in, however, forcing longtime Sunni residents to flee and changing the population balance in favor of Shiites.

As violence spiraled closer to civil war this month, it also took an ominous new course with the outbreak of fighting among Shiites -- the Mahdi Army and its rival Badr Brigade militia, the armed wing of the Supreme Council for the Islamic Revolution in Iraq, or SCIRI.

Both groups are believed to receive training, arms and money from the Shiite theocracy that runs neighboring Iran. Much of the top SCIRI leadership and Badr Brigade chieftains took refuge in Iran during Saddam's Hussein's rule, which was marked by brutal persecution of Shiites.

Gunfights between the two militia groups broke out Saturday in Hamza al-Gharbi, about 60 miles south of Baghdad, after a bomb exploded near SCIRI offices. SCIRI supporters accused Madhi Army fighters of setting off the blast, police Capt. Muthana Khalid Ali said.

At least two people were killed and four injured in the fighting, said another police official, who spoke on condition of anonymity for fear of reprisals.

Ali said Iraqi army and police called for backup from American forces, who imposed a curfew on the city. There was no immediate confirmation of US involvement from military spokesmen.

The new bloodshed came after Iraqi security forces reasserted control over the southern city of Amarah, where rogue members of the Mahdi Army briefly seized control Friday. Twenty-five gunmen and police died in gunbattles before the Iraqi army moved in to retake the city, where the security forces are dominated by members of the Badr Brigade.

The Shiite-on-Shiite violence was particularly alarming because the groups' political wings both back Prime Minister Nouri al-Maliki and Shiites are dominant in parliament. Further conflict between the militias could wreck Shiite unity and bring down al-Maliki's government.

The prime minister is already under heavy US pressure to disband the militia networks. He has not responded and this week even ordered the American military to release a key al-Sadr lieutenant who had been detained on suspicion he was involved in sectarian killings.

Until February, violence in Iraq had largely been the work of Sunni Muslim insurgent attacks on US forces or Shiites. But the Feb. 22 insurgent bombing of a major Shiite shrine in Samarra unleashed a rampage of sectarian killings among Shiites and Sunnis.

Iraq's main Sunni Arab party on Saturday strongly backed an accord signed the day before between Sunni and Shiite religious figures in Islam's holiest city, Mecca. Organizers say they aim only to stop sectarian killings, rather than impose a truce to halt attacks against US forces.

Elsewhere, US forces said they killed a key coordinator of foreign fighters under al-Qaida in Iraq in a raid in Ramadi west of Baghdad. They said the man, who was not identified by name, had been responsible for providing weapons and financing to foreign fighters in the country, as well as producing and distributing video clips and other propaganda.