At least 26 people were killed Friday when gunmen stormed a Baghdad police station and a suicide bomber targeted a Shiite mosque, exacerbating fears that unrest will mar Iraq’s key elections in January.

As the NATO chief opened the alliance’s Baghdad headquarters on what was the deadliest day in the capital since September 30, Ukrainian MPs voted to recall their country’s 1,600 troops serving in Iraq.

The latest killings, claimed by the Al-Qaeda group of Abu Musab al-Zarqawi, Iraq’s most wanted man, came a day after US Defence Secretary Donald Rumsfeld admitted he had underestimated the Iraqi insurgency.

At least 12 policemen were killed in a commando-style raid on the police station in the Al-Amel neighbourhood, medics said, while at least another 14 people died in a suicide car bombing in the northern district of Al-Adhamiya.

One police officer said about 60 men pulled up in cars, minibuses and taxis, circled the building and opened fire with machine guns and rocket-propelled grenades.

"The attackers entered the building when police ran out of ammunition, and they took several policemen up to the roof where they were killed with a bullet to the head," said the officer, who did not give his name.

Interior ministry spokesman Sabah Kadhem said the attack was "part of a strategy of increasing terrorist attacks in order to prevent general elections being held". Landmark elections are due to be held in Iraq on January 30.

The suicide bombing two hours later in the Sunni Muslim district of Al-Adhamiya, near a Shiite mosque, killed 14 people and wounded 19, and caused extensive material damage, an interior ministry source said.

Both attacks were purportedly claimed by Zarqawi’s organisation, the Al-Qaeda Group of Jihad in the Country of Two Rivers, on an Islamist website.

Baghdad had been relatively calm since US-led Iraqi forces launched an assault against the Sunni insurgent stronghold of Fallujah, on November 8.

It was the worst attack in Baghdad since more than 40 people were killed, most of them children, in two suicide bombings in Al-Amel on September 30.

Faced with the violence, visiting NATO Secretary General Jaap de Hoop Scheffer stressed the importance of holding elections as planned, "to see people taking their fate into their own hands."

NATO’s spokesman in Baghdad, Colonel Petter Lindqvist, said "perhaps a hundred" Iraqis had benefited from military training, in Iraq and abroad, in what he called "remarkable" progress.

Several hundred instructors are due to train 1,000 officers a year in Iraq. NATO at present has 20 instructors in the country. Norway also announced that it would send military instructors to Iraq as part of the NATO programme.

In northern Iraq, six people were killed-five of them when mortar rounds, followed by automatic arms fire, targeted the provincial government offices in Mosul, the country’s third-largest city.

Two US soldiers were killed in two separate convoy attacks near the oil-rich city of Kirkuk and in Baghdad, the military said.

Meanwhile, the US military said an offensive in the so-called "triangle of death" south of Baghdad had ended Wednesday, saying 204 insurgents had been rounded up and 11 arms caches discovered.

Operation Plymouth Rock, which involved 5,000 US marines, British troops and Iraqi forces was aimed at flushing out rebels thought to have fled Fallujah.

On the diplomatic circuit, Prime Minister Iyad Allawi extracted German promises to step up efforts to rebuild his battered nation as Germany thwarted an alleged plan to attack him by arresting three Islamic extremists.

Allawi began his latest European tour by meeting German Chancellor Gerhard Schroeder and Foreign Minister Joschka Fischer to discuss sorely needed investment for Iraq.

Interim President Ghazi al-Yawar left for Washington, where he is scheduled to meet US President George W. Bush on Monday to discuss security and the January 30 elections.

Engulfed in political chaos, MPs in US-led coalition member Ukraine voted by 257 votes to 397 in favour of withdrawing their troops based in Iraq.

Washington is to boost US forces to their highest post-war levels before the elections, which Baghdad and Washington have so far refused to postpone.

And in Dubai, Venezuelan President Huge Chavez lashed out at the United States, accusing Washington of unleashing "real terrorism" in Iraq, in an interview broadcast on Al-Jazeera television.