|There are currently about 50,000 US troops in Iraq, operating in 'support and advisory' roles [GALLO/GETTY]
Three suicide bombers have attacked a police headquarters in the northern Iraqi city of Mosul, killing the commander and three other officers.
Officials speaking on condition of anonymity said three men with explosive vests attempted to blow up a police compound housing Iraq's First Police Battalion on Wednesday.
Police shot one of the bombers as the three approached the complex in the early morning attack. Two managed to get inside and blow themselves up, killing Lt Col Shamil Ahmed Oglah, the battalion's commander.
A hospital official confirmed the fatality, but there was no word on the injured.
Al Jazeera's Rawya Rageh, reporting from Baghdad, said that the attack "brought down, essentially, the entire building".
"This happened in the early hours of this morning and until now, rescue teams are still trying to pull bodies and survivors from under the rubble.," she said.
"We understand that in addition to the police commander, at least three other police officers were killed."
Militants had tried to kill Lt Col Ahmed several times in the past, security official Abdul-Raheem al-Shemari told the AP news agency.
The Al Qaeda-linked 'Islamic State of Iraq' group has claimed responsibility for the suicide bombing, the AP news agency reported.
"The attack was carried out by Al Qaeda members because the lieutenant colonel coordinated an operation against Al-Qaeda in the last week," a police officer told the AFP news agency.
In a separate incident on Wednesday, five civilians were wounded when a roadside bomb hit an Iraqi police patrol in eastern Baghdad, police and hospital officials told AP.
Finally, a government-backed Sahwa (Awakening movement) leader escaped unharmed when a bomb attached to his car exploded in Baghdad's southern Doura district on Tuesday, an interior ministry source said.
Mounting security concerns
Assailants frequently target Iraq's security forces as US troops prepare to leave by the end of 2011, and our correspondent says that these attacks are intended to undermine Iraqi law enforcement.
"Now, there hasn't been a lot of attacks since the government was sworn in seven days ago, but attacks have been stepped up against the Iraqi security forces, with targeted assassinations and continued explosions targeting their different headquarters across the country," our correspondent said.
Iraq's leaders are investigating the possibility of removing some of Baghdad's hundreds of unpopular checkpoints because of the improving security situation.
Nouri al-Maliki, the Iraqi prime minister, asked commanders on Tuesday to evaluate the security situation in Baghdad and decide which of the roughly 870 checkpoints that dot the city can be removed.
The checkpoints are manned by Iraqi soldiers and police and designed to catch anti-government fighters, but they also slow down traffic in the already congested city.
The development comes amid remarks by al-Maliki that US troops, which provide security back-up for Iraqi government forces, must leave the country by the end of 2011.
He told the Wall Street Journal newspaper there will be no extension to the planned US withdrawal. It was his first Western media interview since he began a second term as prime minister, nine months after inconclusive elections.