In a daring ambush, insurgents blasted a US patrol with a roadside bomb and showered survivors with gunfire from a mosque in increasingly lawless Mosul. Five American soldiers were killed in the explosion - even as Iraqi troops moved into the northern city to challenge al-Qaida in Iraq. Iraqi reinforcements, along with helicopters, tanks and armored vehicles, converged on Mosul for what Prime Minister Nouri al-Maliki pledged would be a decisive battle against al-Qaida in its last major urban stronghold. The attack Monday on the US patrol - the deadliest on American forces since six soldiers perished Jan. 9 in a booby-trapped house north of Baghdad - raised the Pentagon's January death count to at least 36. The toll so far is 56 percent higher than December's 23 US military deaths and marks the first monthly increase since August. But the figures remain well below monthly death tolls of more than 100 last spring. Tensions in Mosul, Iraq's third largest city, have spiked after an explosion last week in an abandoned apartment that authorities say was used to stash insurgents' weapons and bombs. As many as 60 were killed and 200 injured. The unrest in Mosul stands in sharp contrast to a significant decline in bloodshed most elsewhere in Iraq in recent months. The relative calm has been credited to a US-led security crackdown - along with a Sunni revolt against al-Qaida in Iraq and a cease-fire order by radical Shiite cleric Muqtada al-Sadr for his powerful Mahdi Army militia. But influential members of al-Sadr's movement said Monday they have urged the anti-US cleric to call off the six-month cease-fire when it expires in February - a move that could jeopardize the security gains. In Mosul, the attackers struck in the southeastern Sumar neighborhood, a middle-class district popular with former officers in Saddam Hussein's military and now a suspected hotbed for the insurgency. After the roadside bomb blew apart the American vehicle - killing the five soldiers - gunmen opened fire from a mosque. A fierce gunbattle erupted as US and Iraqi soldiers secured the area, the military said. Iraqi troops entered the mosque but the insurgents had already fled, according to a statement. "The insurgents are willing to desecrate a place of worship by using it to attack soldiers to further their agenda," said Maj. Peggy Kageleiry, a US military spokeswoman in northern Iraq. There was other fighting in the neighborhood. An Iraqi officer, speaking on condition of anonymity because he was not authorized to release the information, said three civilians were wounded and helicopters bombarded buildings in the district, the scene of frequent attacks on US and Iraqi forces. Also Monday, insurgents attacked four policemen heading home from work south of Mosul, killing two and wounding the other two, Nineveh provincial police said. US commanders have described Mosul as the last major Iraqi city with a significant al-Qaida presence, although they have warned that insurgents remain a potent force in rural areas south and northeast of Baghdad. But the military has said Iraqi security forces will take the lead in the city - a major test of Washington's plans to someday shrink the American force and leave it as backup for Iraqi security forces. Al-Qaida and its supporters would find themselves without a major base of operations if ousted from Mosul, which occupies transport crossroads between Baghdad, Syria and other points. But the fight is expected to be difficult. Mosul has not seen the groundswell of Sunni anger against al-Qaida that has helped turn the tide against insurgents in Anbar province and other areas. Monday's attack was the deadliest roadside bombing since Nov. 5, when four soldiers were killed by a blast that destroyed their Humvee in the northern Tamim province of which Kirkuk is the capital. In Shiite areas to the south, some top advisers to the cleric al-Sadr have urged him to drop the cease-fire order for his Mahdi Army when it expires next month. The critics are angry over ongoing campaigns by US and Iraqi forces against so-called rogue fighters who have refused to put down their weapons. Al-Sadr's followers claim the US-Iraqi raids are a pretext to crack down on the wider movement, which has pulled its support for the Washington-backed government. The maverick cleric announced earlier this month that he would not renew the order unless the Iraqi government purges "criminal gangs" operating within security forces he claims are targeting his followers. That was a reference to rival Shiite militiamen from the Badr Brigade who have infiltrated security forces participating in the ongoing crackdown against breakaway militia cells the US has said were linked to Iran. The political commission of al-Sadr's movement - along with some lawmakers and senior officials - said they were urging the cleric to follow through with his threat, pointing to recent raids against the movement in the southern Shiite cities of Diwaniyah, Basra and Karbala. "We presented a historic opportunity when we froze the (Mahdi) army," Nasser al-Rubaie, leader of the Sadrists in parliament, told reporters. "But they didn't take advantage of it." The group planned to send a formal message to al-Sadr's main office in the holy city of Najaf, two Sadrist legislators and a member of the political commission told The Associated Press. They spoke on condition of anonymity because of fears of retribution. Al-Sadr's political commission is made up of the movement's most powerful officials, whose opinion often reflects that of the reclusive cleric. But the officials stressed that he retains sole decision-making authority over the militia. Mahdi Army militiamen fought US troops for much of 2004, and al-Sadr has tirelessly called for the withdrawal of US forces from Iraq.