The US President, George W Bush, has said the complete withdrawal of US forces from Iraq will be a decision for future presidents and governments of Iraq to make.

Mr Bush refused again to give any timetable for a reduction in the 130,000 US soldiers still serving in the region three years on from the start of the US-led invasion, instead indicating they could be there for some time.

Mr Bush was speaking at an extensive White House press conference to mark the third anniversary of the US-led invasion of Iraq.

He said he did not believe Iraq was sliding into civil war. He said part of the proof was that the Iraqi Army had not fragmented along ethnic lines.

He said the US was committed to staying on the offensive in Iraq as it was part of the global war on terror and that if the US withdrew, what he called Islamofacists would be emboldened. 

Meanwhile in Iraq, at least 18 policemen and four civilians have been killed after insurgents stormed a police station in the town of Muqdadiya, north of Baghdad.

Iraqi police said that 10 of the estimated 100-strong group of insurgents were also killed.

It is understood 33 detainees suspected of terrorist activities were freed in the raid.

The attackers, who were equipped with rocket-propelled grenades, mortars and assault rifles, set fire to the police station before escaping.

The gunmen also seized radio equipment, rendering the rest of the police network insecure and hampering the response to the attack. 

Investigation into civilian deaths in Iraq

Separately, the US military has confirmed that it has begun a criminal investigation into allegations that marines shot dead 15 Iraqi civilians last year.

The deaths occurred last November after a roadside bomb exploded in the town of Haditha, killing one marine and injuring two others.

A statement from US officials at the time said the 15 civilians were also killed by the blast.

But a preliminary military investigation conceded that those who died were shot by US marines in their homes.

Criminal investigators for the US Navy will now seek to establish whether the 12 marines involved were guilty of misconduct.

The investigation was launched after the case was raised by Time magazine.

US military probes Iraqi police allegations

In another defelopment, the US military has said it is investigating Iraqi police allegations that US soldiers shot dead a family of 11 in their home last week.

Police in Ishaqi, 100km north of the capital, said five children under school age, four women and two men were shot dead by troops in a house that was then blown up.

Local police colonel, Farouq Hussein, claimed autopsies had found that all the victims were shot in the head.

A US military spokesman said the dead included a guerrilla and said they died after troops were fired on from the house as they arrived to arrest an al-Qaeda suspect.