Despite the bombs, leaders of the main Shia and Kurdish alliances announced last night that they had struck a deal to finally allow them to form a government, almost a month after the election results were announced and days before the National Assembly is to meet for the first time.

Under the deal, the new government will begin discussion on the return of more than 100,000 Kurds expelled from Kirkuk by Saddam Hussein. The question of whether the map will be redrawn to return Kirkuk to the area under Kurdish semi-autonomous control will be dealt with later, when the assembly begins drawing up a new constitution.

Jalal Talabani, the Kurdish leader, is expected to be nominated as President, and Ibrahim Jaafari, the Shia politician, is tipped to become the Prime Minister. The surge in violence is blamed on insurgents trying to exploit uncertainty created by the failure to form a new government after the elections in January.

The Shia mosque explosion occurred as mourners gathered for the funeral. “As we were inside the mosque we saw a ball of fire and heard a huge explosion,” Tahir Abdullah Sultan, 45, said. “After that, blood and pieces of flesh were scattered around the place.”

The area was quickly sealed off by American forces, who maintain a heavy presence in the city, and ambulances converged on the scene. Mosul has been a hotbed of insurgent activity, particularly since the blistering assault on Fallujah last November which scattered militants operating there, many of them to the northern city.

Shias have long been targets of the most extreme insurgent groups, such as that led by Abu Musab al-Zarqawi, which have vowed to try to ignite civil war between the Sunni minority and the Shia majority.

Insurgents associated with al-Zarqawi claimed to be behind the murder of Lieutenant-Colonel Ahmed Beis, the Baghdad police chief killed as he drove to work at Salhiya police station, close to the heavily protected green zone. His car was stopped at what appeared to be a regular police checkpoint. As soon as he offered his identity papers, uniformed men sprayed his car with bullets, killing him and two other policemen in the car.

Another attacker in police uniform filmed the attack.

The policemen’s murder is one in a series of attacks in which insurgents have posed as police officers. While some may have bought uniforms in markets, there is evidence that insurgents are continuing to penetrate the ranks of security forces, despite attempts by the Interior Ministry to stop them.

Only hours after yesterday’s killing, four Defence Ministry employees were arrested on suspicion of passing information to rebels on the movements of ministry officials.

“It is worse than ever,” a police captain in Baghdad said. “You do not know who to trust. They are so desperate to recruit people into the force, they are taking anyone. It’s just too easy for the insurgents to get in.”

Lax background checks, rampant corruption and intimidation by insurgents were the most common methods of infiltrating the force, he said. In some cases, insurgents themselves had bribed officers to get past background checks to join the force, often just long enough to gather information for an attack before quitting. Infiltration of the National Guard was blamed for last October’s massacre of nearly 50 army recruits as they travelled home from training.

Sabah Kadhim, an Interior Ministry official, denied that the problem was getting worse. “When we started our work there was a lot of it because the Americans were taking anyone off the streets, so people who wanted to work for terrorists just had to show up,” he said.

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