A wave of coordinated bomb attacks in Iraq, which have killed at least 68 people, have prompted fears that a government rift is deepening sectarian and ethnic divisions.

The bombings took place just days after the last U.S. troops left Iraq. Most of the areas targeted were Shiite districts, according to Iraqi officials.

No group has claimed responsibility.

The attacks came as political friction between the Sunni and Shiite factions of the coalition government increase, threatening the stability of the country.

Iraq's borders were drawn up by the colonial powers in the 1920s, leaving the territory divided along ethnic and sectarian lines.

The country's south is mainly made up of Shiites while the west is predominantly Sunni. The semi-autonomous Kurdistan is in the north.

Kurdistan's oil reserves have sparked increasing tensions between the region's leaders and Baghdad.

Sunni Iraqis have also voiced concerned over what they perceive as a rise of authoritarianism within the government.

The recent political dispute between the Shiite Prime Minister Nouri Maliki and the Sunni Vice President Tariq al-Hashemi has added to pressures.

Sunnis politicians complain Maliki is using his position to advance Shiite interests.

Maliki has called for an arrest warrant against Hashemi, and accused him of running a death squad that targeted officials from the government.

The vice president has denied the accusations. He blamed the latest wave of bombings on Maliki, telling the BBC: "We should blame Mr Maliki, he started a national crisis and it's not easy to control.

"The Iraqis have a right to be worried."