Afghanistan's Civil Aviation Minister, Mirwais Sadiq, has been killed in the western city of Herat.
Ismail Khan is one of the most powerful men in Afghanistan
State TV said Mr Sadiq died after a rocket propelled grenade hit his car.
The attack followed a failed bid to kill his father, the governor of Herat.
Heavy fighting broke out after Mr Sadiq's death between troops loyal to his father and a senior local military commander Zahir Nayebzada, police said.
There are reports that up to 100 people have been killed in the clashes.
A spokesman for Herat governor Ismail Khan blamed Mr Sadiq's death on forces loyal to Zahir Nayebzada.
Mr Nayebzada, for his part, accused Ismail Khan's forces of provoking the fighting by trying to take command of his division. He said Mr Sadiq was killed after breaking into his residence.
Troops loyal to Mr Khan have surrounded the commander's home as well as a military barracks in the city.
In Kabul, President Hamid Karzai's cabinet convened an emergency session following Mr Sadiq's death.
A government statement said Mr Karzai was "deeply shocked" by the killing and had ordered an investigation. The government said it was sending a senior delegation to Herat.
Man of power
State television has reported that the security commander for Herat, the city's director of narcotics control and a bodyguard were travelling in the car with the minister and were also killed in the attack.
Ismail Khan, a former anti-Soviet resistance commander, is one of the most powerful men in Afghanistan with a strong following among ethnic Tajiks and a private army.
Correspondents say President Karzai has virtually no influence in the province, where Mr Khan has dominated since the end of Taleban rule in late 2001.
Mirwais Sadiq is the third minister under President Hamid Karzai to be assassinated.
His predecessor as aviation minister, Abdul Rahman, was beaten to death at Kabul airport in February 2002.
Vice President and Public Works Minister Haji Abdul Qadir was shot dead outside his office in July 2002.
Last February, Minister for Petroleum and Mines Juma Mohammad Mohammadi died in an air crash off Pakistan.
Security around the president has been tight since a failed assassination attempt in the southern city of Kandahar in September 2002