BAGHDAD, July 18 (Xinhua) -- Four people were killed and eight others wounded in attacks in Iraq on Thursday, while two al-Qaida cell leaders were arrested in the eastern part of the country, police said.

Early in the morning, gunmen using silenced weapons broke into the house of a farmer and shot him dead at a village near the city of Balad, some 80 km north of the Iraqi capital of Baghdad, a local police source told Xinhua on condition of anonymity.

Later on, a roadside bomb went off when a police force arrived at the scene, wounding four policemen, the source said.

In a separate incident, a farmer and his wife were killed when a bomb attached to their car detonated in the city of Dujail, some 60 km north of Baghdad, a local police source anonymously told Xinhua.

Elsewhere, four policemen were wounded in a roadside bomb explosion near their patrol in the town of Sulaiman Beg, some 170 km north of Baghdad, a local police source said.

In Iraq's eastern province of Diyala, gunmen shot dead a civilian in the town of Abu Saiyda, in the northeast of the provincial capital city of Baquba, some 65 km northeast of Baghdad, a provincial police source told Xinhua on condition of anonymity.

Separately, Iraqi security forces arrested a leader of a local al-Qaida cell in western Baquba, who is believed to be an expert in bomb making, the source said.

Meanwhile, the security forces captured another leader of an al- Qaida cell in the town of Wajihiyah, 25 km northeast of Baquba, the source said, adding that the suspect is believed to be involved in violent attacks against civilians in the town.

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