Four people were killed and six wounded Tuesday in separate attacks in eastern and northern Iraq, police said.

In Iraq's eastern province of Diyala, two people were killed and four wounded in a bomb explosion at a residential area in Himreen area, about 55 km northeast of the provincial capital city of Baquba, a provincial police source told Xinhua on condition of anonymity.

An armed man believed to be linked to al-Qaida was killed during a clash when his group attacked a checkpoint manned by fighters of government-backed Sahwa paramilitary group outside the city of Maqdadiyah, some 40 km northeast of Baquba, the source said.

The Sahwa militia, also known as the Awakening Council or the Sons of Iraq, include some former anti-US Sunni insurgent groups, who turned their rifles against al-Qaida after finding out the network exercised indiscriminate killings against both Shiite and Sunni communities.

Separately, a civilian was critically wounded by gunmen near Baquba, the source added.

Diyala province, which stretches from the eastern edges of the capital Baghdad to the Iranian border, has long been a volatile area since the US-led invasion of Iraq in 2003 despite repeated military operations against the militant groups.

Elsewhere, unidentified gunmen shot dead a civilian in the city of Samarra, some 120 km north of Baghdad, a local police source anonymously told Xinhua.

In addition, a Sahwa fighter was seriously wounded by gunmen in the city of Shirqat, some 280 km north of Baghdad, a local police source said.

Iraq is witnessing its worst eruption of violence in five years, which raised fears that the country is sliding back to a full- blown civil conflict that peaked in 2006 and 2007, when monthly death toll sometimes exceeded 3,000.