Mortar fire killed four officers and two soldiers near Baghdad and 11 people died in violence elsewhere Monday as officials said unrest in Iraq was fuelled by the Syrian war.

A brigade commander was among those killed by the mortar attack on an Iraqi army base in the Abu Ghraib area west of Baghdad, security officials said.

Two days before, five senior officers, including a division commander, and 10 soldiers were killed during an operation against militants in the mainly Sunni western province of Anbar.

Bombings and shootings in Baghdad also killed at least nine people and wounded 21 on Monday, while violence elsewhere in the country left two more people dead and eight wounded.

Violence in Iraq has reached a level not seen since 2008, when the country was just emerging from a brutal period of sectarian killings.

The United States on Sunday called for leaders in the region to work to cut funding and recruitment for two jihadist groups -- the Islamic State of Iraq and the Levant, and Al-Nusra Front -- saying foreign fighters were going to Syria and then carrying out attacks in Iraq.

ISIL operates in both Syria and Iraq, while the Al-Nusra Front is based in Syria but has also been linked to Iraq.

The US calls "on regional leaders to take active measures to police the funding and recruitment for these groups... and deter the flow of foreign fighters into Syria, many of whom later conduct suicide bombings against innocent civilians in Iraq," State Department spokeswoman Jen Psaki said.

Iraqi defence ministry spokesman Mohammed al-Askari also said the situation in Syria was driving violence in Iraq.

Askari told AFP that aerial photographs and other information pointed to "the arrival of weapons and advanced equipment from Syria to the desert of western Anbar and the border of Nineveh province," referring to two Sunni-majority areas that border Syria.

This has encouraged Al-Qaeda-linked militants to "revive some of their camps that were eliminated by security forces in 2008 and 2009," Askari said, adding that aerial photos showed 11 militant camps near the border with Syria.

"Photographs and intelligence information indicate that whenever there is pressure on armed groups in Syria, they withdraw to Iraq... to regroup and then carry out terrorist operations in the two countries," Askari said.

Prime Minister Nuri al-Maliki meanwhile said on Sunday that a Sunni Arab anti-government protest camp in Anbar has become a "headquarters for the leadership of Al-Qaeda," calling on legitimate protesters to leave before security forces move in.

Protests broke out late last year in Sunni-majority areas of Iraq, where people complain of being both marginalised by the Shiite-led government and unjustly targeted by heavy-handed security measures.

Experts say that widespread Sunni anger has been a major factor in the heightened unrest this year.

Death tolls from violence surged after security forces raided an anti-government protest site near the northern town of Hawijah on April 23, sparking clashes in which dozens died.

More than 6,650 people have been killed in Iraq since the beginning of the year, according to AFP figures based on security and medical sources.