Iraq security forces 'struggling' against bombers

Protesting Shiite pilgrims poured into a holy city south of Baghdad today amid relentless attacks that have killed more than 170 people in Iraq this week.

The top US commander in Iraq acknowledged the deadly power of suicide bombers.

"We share the horror" of witnessing the bloodshed, said US Gen. David Petraeus in his first news conference since taking charge of US. Forces in Iraq last month.

But Petraeus noted that security teams were often at the mercy of suicide bombers who have blended into the vast pilgrim processions.

"It is an enormous task to protect all of them," Petraeus told reporters in Baghdad's heavily fortified Green Zone, adding: "If someone is willing to blow up himself … the problem becomes very, very difficult indeed."

The attacks are part of a wider offensive by suspected Sunni insurgents since a US-led security crackdown began in Baghdad last month.

The Pentagon has pledged 17,500 combat troops for the capital. Petraeus said "it was very likely" that additional US forces will be sent to areas outside the capital where militant groups are regrouping, including the Diyala province north-east of Baghdad.

The region has become an increasingly important staging ground for groups including al-Qaida in Iraq. Meanwhile, many Sunni extremists apparently have shifted to Diyala to escape the Baghdad clampdown.

Petraeus declined to predict the size of the expected Diyala reinforcements. But he stressed that military force alone was "not sufficient" to end the violence in Iraq and political talks must eventually include some militant groups now opposing the US-backed government.

"This is critical," said Petraeus, noting that such negotiations "will determine in the long run the success of this effort".

One of Iraq's most expansive militias - the Mahdi Army of radical Shiite cleric Muqtada al-Sadr - appears to have set aside its weapons under intense government pressure to lend support to the Baghdad security plan.

Madhi militiamen also have allowed Iraqi authorities to try to protect at least one million pilgrims heading to Karbala, about 50 miles south of Baghdad.