The Islamic State jihadist group claimed responsibility on Sunday for the deadliest spate of bombings to strike the Iraqi capital in weeks, saying a "Baghdad cell" helped carry out the attacks.

Seven different explosions in six mainly Shiite districts of Baghdad killed at least 24 people on Saturday, with the Islamic State claiming four of the blasts - two suicide attacks and two car bombs.

The group, which last month proclaimed a "caliphate" straddling Syria and Iraq, said the two suicide bombers were a German and a Syrian and that they targeted checkpoints manned by soldiers, police and allied Shiitemilitiamen.

"Two knights of the knights of Islam and heroes of the caliphate were launched, Abu Qaqa al-Almani and Abu Abdulrahman al-Shami, to destroy check-points and dens of the... government," it said in an unverified statement posted online.

The Sunni extremist group, which controls large parts of north and western Iraq since a June 9 offensive, carries out frequent attacks in Baghdad.

Saturday's near-simultaneous attacks were carried out "in coordination with a Baghdad cell", the group said. The Islamic State claimed a toll of more than 150 dead and wounded, without giving a breakdown.

Police and medical sources told AFP on Saturday that at least 24 were killed and 75 wounded in the Baghdad explosions.

Islamic State, the militant group that seized large parts of northern Iraq last month, has claimed several suicide bombings in the capital.

Its latest claim was for a bombing that killed three people on Thursday in the heart of the city.

Baghdad has seen few attacks compared with the violence in other areas hit by the Islamic State's offensive last month, though bombs still hit the capital on a fairly regular basis.

The civilian toll, mainly from fighting between government forces and the Sunni insurgents, this year has been huge.

At least 5,576 Iraqi civilians have been killed since January, when Sunni insurgents led by an al-Qaida off-shoot now known as the Islamic State, overran the city of Falluja in the western province of Anbar, the United Nations said on Friday.

The UN said more than 1.2 million people have been displaced this year. More than 600,000 of them have fled their homes since early June.

The patchwork of Sunni insurgents led by Islamic State that swept across northern Iraq last month reached to within 70 km of Baghdad. The army and allied Shiite militia have been trying since then to regain the territory.

Militants fought off an army offensive to retake the northern city of Tikrit on Tuesday.

The army was forced to pull back south of the city on the banks of the Tigris.

Intense fighting has raged for days northwest of Tikrit around a military base known as Camp Speicher, once one of the main US headquarters.

Islamic State wrote on an affiliated Twitter feed on Thursday it had shot down two helicopters during a battle around the base.

Prime Minister Nouri al-Maliki's military spokesman said on Saturday that government forces were fully in control of the base.

The fighting has exacerbated a political crisis in Baghdad, where al-Maliki is trying to form a government in the face of opposition from Sunnis, Kurds and some Shiites, three months after Iraq held a parliamentary election.

AFP - Reuters