Violence has claimed the lives of 2,417 Iraqis in June, making it the deadliest month so far this year, the UN said on Tuesday, underlining the daunting challenge the government faces as it struggles to confront Islamic extremists who have seized large swaths of territory in the north and west.

In recent weeks, fighters from the Islamic State of Iraq and Syria have spearheaded a lightning offensive across Iraq, plunging it into its deepest crisis since the last U.S. troops left in 2011. The al-Qaeda breakaway group now controls territory stretching from northern Syria as far as the outskirts of Baghdad in central Iraq.

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In addition to the thousands of dead, tens of thousands of Iraqis have been internally displaced or have become foreign refugees as they flee the violent advance of ISIS. (Ahmed Jadallah/Reuters)

The figures issued by the UN mission to Iraq put last month's civilian death toll at 1,531, with 886 security forces killed. UNAMI added that 2,287 Iraqis, including 1,763 civilians, were wounded.

The figures exclude deaths in embattled Anbar province, which is largely controlled by Sunni militants.

The second deadliest month this year was May, with 799 Iraqis killed, including 603 civilians. April's death toll was 750.

The latest casualty figures exceed even last year's peak. The UN reported that last July at least 1,057 Iraqis were killed and another 2,326 were wounded.

"The staggering number of civilian casualties in one month points to the urgent need for all to ensure that civilians are protected," the UN Special Representative in Iraq, Nickolay Mladenov, said in the statement.

Mladenov called on Iraqi political rivals to "work together to foil attempts to destroy the social fabric of Iraqi society."

Islamic State declares caliphate

Iraq's new parliament holds its inaugural session Tuesday. The country's top Shiite cleric urged lawmakers last week to agree on a prime minister before meeting in hopes of averting months of wrangling that could further destabilize the country.

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ISIS militants in Iraq and Syria have held parades to celebrate the declaration of a caliphate and display the weapons of war they have seized from government forces in both countries. (Reuters)

The Islamic State meanwhile announced the establishment of its own government, or caliphate, ruled by Islamic law. It proclaimed its leader, Abu Bakr al-Baghdadi, a highly ambitious Iraqi militant with a $10 million U.S. bounty on his head, to be the caliph, and it demanded that Muslims around the world pledge allegiance to him.

Through brute force and meticulous planning, the Sunni extremist group — which said it was changing its name to simply the Islamic State, dropping the reference to Iraq and the Levant — has managed to effectively erase the Syria-Iraq border and lay the foundations of its proto-state. Along the way, it has battled Syrian rebels, Kurdish militias and the Syrian and Iraqi militaries.

U.S. sends 300 more troops

Officials said Monday the U.S. is sending another 300 troops to Iraq to increase security at the U.S. embassy and elsewhere in the Baghdad area to protect U.S. citizens and property.

That raises the total U.S. troop presence in Iraq to approximately 750, the Pentagon said.

The State Department, meanwhile, announced that it was temporarily moving an unspecified "small number" of embassy staff in Baghdad to U.S. consulates in the northern city of Irbil and the southern city of Basra. This is in addition to some embassy staff moved out of Baghdad earlier this month,