KIRKUK, Iraq (AFP) - More than 20 people were killed in car bomb attacks, as Islamist militants threatened separately to kill 10 people employed by a Turkish-US business and two Americans and one Briton.
A US air strike killed four people and left five wounded in Fallujah, as the US military kept up its campaign of nightly attacks in the Iraqi rebel stronghold, a local hospital said.
The US military said a precision strike was carried out on an checkpoint in northern Fallujah operated by gunmen linked to suspected Al-Qaeda operative Abu Mussab al-Zarqawi.
More than 400 Iraqis have perished in a wave of suicide bombings and clashes 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 bloodshed, a suicide bomber smashed through the security barriers outside an Iraqi national guard headquarters in Kirkuk, 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.
Within 30 minutes of the attack, a US convoy responding to the emergency was hit by a car bomb, killing two American soldiers.
The Baghdad bombings, along with another in the capital Friday that killed five people, was claimed in an Internet message by Zarqawi's militant Tawhid wal Jihad (Unity and Holy War) organization.
Zarqawi loyalists 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, were being held in the country.
Americans Jack Hensley and Eugene "Jack" Armstrong and British engineer Kenneth Bigley were abducted Thursday by gunmen from their Baghdad home.
In another kidnapping, an Islamist group threatened to kill 10 employees of a US-Turkish company unless the firm halted its operations in Iraq within three days, Al-Jazeera reported.
Al-Jazeera said the group, calling itself the "Salafist Brigade Abu Bakr al-Seddiq", did not name the men's company.
In a bizarre twist, an Islamist radical group claimed in a statement it was releasing two French journalists, abducted one month ago, for them to cover the "activities of the resistance."
But it was impossible to confirm the statement's authenticity.
Christian Chesnot and Georges Malbrunot were seized along with their Syrian driver, Mohammed al-Jundi, on August 20 by the Islamic Army in Iraq.
In another development, 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 himself 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.
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 latest deadly US strike in Fallujah, which lies in Al-Anbar province, followed an air raid Friday that killed three people and several bombardments the previous night that left 44 dead around the city, including women and children.
US forces defend the strikes as targeting hideouts of Zarqawi militants.
In southern Iraq, British troops killed three Shiite Muslim militiamen in clashes before coalition forces withdrew from the office of radical cleric Moqtada al-Sadr in the port city of Basra, the military said.
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, before returning to the Jordanian capital.
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.
Meanwhile, the Observer newspaper reported Britain is to scale back its 8,000-strong military presence in southern Iraq in October, despite fears of worsening security.
It said the drawdown will take place when the First Mechanized Infantry Brigade is replaced by the Fourth Armoured Division, currently based in Germany, in a routine rotation.
The Observer's report contradicted one in the Times newspaper, which said Britain was considering whether to send "a few extra troops" to Iraq ahead of the elections taking place in January.