KIRKUK, Iraq (AFP) - At least 18 people were killed in a suicide bombing, capping a week of carnage in Iraq, as Al-Qaeda-linked militants threatened to kill two American hostages and a Briton in 48 hours.
More than 400 Iraqis have perished in a wave of bombings and fighting since the start of the month, exacerbating fears over the security situation in the run-up to general elections due to be held in January.
In the latest attack, a suicide bomber smashed through the security barriers outside an Iraqi national guard headquarters in Kirkuk, in what was the second major strike in the fractured northern oil city in two weeks, police said.
At least 18 people were killed and another 63 wounded, hospital officials said.
The vehicle passed through three barriers before it reached the outer gate of the building and exploded, sending shrapnel flying into a crowd of national guard recruits lined up outside.
A car bomb also hit a US convoy on the main Baghdad airport road, killing an Iraqi and wounding three soldiers -- a scene all too familiar in Iraq, where the health ministry reported 268 killed in the past week alone and another 820 wounded.
Meanwhile, loyalists of suspected Al-Qaeda operative Abu Mussab al-Zarqawi threatened to kill two Americans and a Briton unless Iraqi women prisoners are freed within 48 hours, according to a videotape broadcast on Al-Jazeera television.
The US military said only two Iraqi women, both of them high-security detainees believed to have been instrumental in ousted president Saddam Hussein`s weapons programmes, are being held in the country.
Three blindfolded men were shown sitting in front of gunmen dressed entirely in black, pointing their guns at the pale-faced hostages.
Americans Jack Hensley and Eugene "Jack" Armstrong and British engineer Kenneth Bigley were abducted by gunmen from their Baghdad home on Thursday.
Zarqawi militants have previously claimed to have executed four foreign hostages, an American, a Turk, a South Korean and an Egyptian. Last month, they freed two Turks after the men`s firm agreed to stop supplying US forces in Iraq.
In further violence, five bodyguards for Mohammed Ahmed Zebari, a senior oil ministry official in Mosul, died in a hail of gun and rocket-propelled grenade fire in the northern city, said police. Zebari emerged unscathed from his car.
In the Sunni Muslim insurgent bastion of Samarra, a woman and two children were killed in a mortar attack, while a child died when a bomb exploded near his home in the Shiite Muslim city of Hilla, south of Baghdad, medical sources said.
Again in the Kirkuk area, gunmen shot dead a Shiite Arab tribal leader. Sheikh Khadem al-Hani was killed and two of his bodyguards wounded when gunmen ambushed them north of the city, said police.
Kirkuk, home to a mix of Kurds, Arabs and Turkmen, is a volatile city, haunted by the spectre of ethnic violence.
In mainly Sunni Muslim western Iraq, the body of the deputy governor of Al-Anbar province was found in a field near the provincial capital Ramadi, a police officer said.
Bassem Mohammed had been kidnapped on September 8 by gunmen who stopped his car and wounded his son in the attack.
The murder was the latest in a string of setbacks in Al-Anbar, where the city of Fallujah has become a no-go zone for US troops.
British troops killed three Shiite Muslim militiamen in clashes on Saturday before coalition forces withdrew from the office of radical cleric Moqtada Sadr in the southern Iraqi city of Basra, the military said.
A Sadr aide had threatened that the cleric`s militiamen would attack British troops occupying the building.
Despite the rampant unrest, national carrier Iraqi Airways launched its first international service in 14 years, with a plane arriving in Baghdad from Amman -- albeit without any passengers.
The same plane also flew to Damascus and back.
The airline had been grounded for commercial operations since Iraq`s 1990 invasion of Kuwait and the subsequent UN sanctions imposed on Saddam`s regime. It has only one functioning plane, a Boeing 737.
On the diplomatic front, an Iraqi ambassador took up his post in Tehran for the first time since the 1980-1988 Iran-Iraq war, Iranian state media said.