BAGHDAD, Iraq (AP) – Insurgents killed 19 Iraqi soldiers and wounded four others in a coordinated ambush northeast of Baghdad just two days after the deadliest attack against US Marines in four months.

The bloodshed confirmed US and Iraqi warnings of a surge in insurgent attacks ahead of national elections set for December 15. A total of 14 US service members have died so far this month, 10 of them in a huge bombing Thursday near Fallujah.

Yesterday’s attack occurred as an Iraqi army unit was on patrol near Adhaim, about 100 kilometres (60 miles) north of Baghdad. Survivors said insurgents triggered a roadside bomb and then showered the patrol with rocket-propelled grenades and machine gun fire.

Earlier this week, President George W Bush outlined his strategy for victory in Iraq, with a key point calling for Iraqi forces to eventually replace US troops in the fight against insurgents.

Elsewhere, the US base at the airport in Mosul, Iraq’s third largest city, came under mortar or rocket fire yesterday, wounding two American soldiers, the US military said.

The US command has released few details of the bombing which killed 10 members of the Marines’ Regimental Combat Team 8, based at Camp Lejeune, North Carolina.

A witness said it occurred at a mill in the village of Amiriyat al Fallujah, just outside the city. The bomb was fashioned out of four large artillery shells, US officials said.

“More than 20 troops entered there and a huge explosion happened,” said Mohsen Mohammed. “Afterward, the helicopters and tanks arrived in the area.”

Later Saturday, Al-Jazeera broadcast a videotape from the Islamic Army of Iraq showing a huge explosion targeting a US foot patrol near Fallujah. The tape did not directly link the explosion to Thursday’s attack, but the Al-Jazeera announcer noted the Marine deaths as the tape aired.

The grainy video, which appeared to have been shot through a long lense, showed ground troops walking down a street on both sides of a Humvee when a huge fireball engulfed the scene, sending terrified Iraqi bystanders scrambling for their lives.

Al-Jazeera said the Islamic Army, one of Iraq’s best-known insurgent groups, also claimed responsibility for a series of other attacks against US forces north of Baghdad, in Nasiriyah and another in Fallujah.

In another video aired by Al-Jazeera, a group calling itself the Mujahedeen of Tal Afar claimed responsibility for destroying a US Bradley Fighting Vehicle in the northern city. The video showed bomb damage to the Bradley but Al-Jazeera said it was unclear whether the footage was authentic.

The United States hopes a big Sunni turnout in the December 15 election will produce a government that can win the trust of the Sunnis, the backbone of the insurgency, and convince more of them to lay down their arms. That would hasten the day US troops could go home.

Iraq’s top Shiite cleric is signalling to his followers that they should vote for the Shiite alliance in the upcoming election, aides said.

Grand Ayatollah Ali al-Sistani had stopped receiving Shiite politicians and candidates weeks ago in a sign of displeasure over the Shiite-led government’s performance. However, aides said the cleric is now telling people to vote for the Shiite alliance to “preserve Iraq’s unity” and “protect Iraqis.”

The aides, who spoke on condition of anonymity because they are not allowed to talk to the media, said al-Sistani is not openly endorsing the United Iraqi Alliance or mentioning it by name.

Meanwhile, the German government said it was making intense efforts to secure the release of an aid worker and her driver kidnapped in Iraq on November 25. In a video made public on Tuesday, kidnappers threatened to kill Susanne Osthoff, 43, unless Germany stops dealing with the Iraqi government.

Foreign Minister Frank-Walter Steinmeier told reporters in Berlin that the government had been unable to establish contact with the kidnappers.

Germany opposed the US-led invasion of Iraq but has been training Iraqi soldiers and police outside this country.

A leading member of the British anti-war movement, Anas Altikriti, arrived Saturday in Iraq to try to win the release of four Christian peace activists – two Canadians, an American and a Briton. Altikriti told the British Broadcasting Corporation, that he would meet with various Iraqi organisations in hopes one of them might have contacts with the kidnappers.

On Friday, Al-Jazeera broadcast a videotape and statement in which the kidnappers threatened to kill the hostages unless all prisoners in US and Iraqi detention centres were freed by December 8.

The Christian activists – Norman Kember, 74, of London; Tom Fox, 54, of Clear Brook, Virginia; James Loney, 41, of Toronto; and Harmeet Singh Sooden, 32, of Canada – had been repeatedly warned by Iraqi and Western security officials that they were taking a grave risk by moving about Baghdad without bodyguards.