KABUL (AFP) - Militants killed four brothers, all police officers, and captured their father in an attack on their home in Afghanistan while a bomb left four civilians dead separately, authorities said Tuesday. The attack in the central province of Ghazni late Monday came as extremist Taliban rebels have stepped up action in an insurgency against the US-backed government of President Hamid Karzai. The rebels, "attacking the house of a man whose four sons served in the national police, killed his four sons and took him to an unknown place," the Interior Ministry said in a statement. Police launched a hunt for the militants to rescue the father of those "brave brothers," the statement said. The ministry blamed the attack on the "opposition," a reference to Taliban and other insurgents trying to destabilise the government. In Khost province on the border with Pakistan a remote-controlled bomb exploded underneath a pick-up truck and killed four people, including a woman and a child, Colonel Muhammad Yaqoub Mondozai said. Three more people were wounded, the deputy provincial police chief said. In the capital Kabul meanwhile a suicide bomber blew himself up near the landmark and ancient Babur's Gardens early Tuesday, wounding five civilians, the Interior Ministry said. There was no claim of responsibility for the attack. In other violence, suspected Taliban militants killed a government spokesman in the eastern province of Paktia late Monday, police said. Ghamai Khan Muhammadyar, the spokesman for the governor of Paktia, was killed after rebels raided his house, another provincial official said. The rebels abducted his brother. Muhammadyar told an AFP reporter in May that Taliban were threatening to kill him because of his work. The Taliban were in government until 2001 when they were ousted in a US-led attack launched when they did not hand over Al-Qaeda fighters for the September 11 attacks on the United States.