The head of Pakistani militant group Lashkar-e-Jhangvi was killed by a US drone air strike in North Waziristan on 24 February, the BBC has learned.
Qari Mohammad Zafar is believed to have led the Sunni Muslim extremist group, which has close links with al-Qaeda and the Pakistani Taliban, since 2005.
Mufti Abuzar Khanjari had now replaced Zafar, militants told BBC Urdu.
Zafar was wanted by US and Pakistani authorities over the March 2006 attack on the US consulate in Karachi.
The US had offered a $5m (£3.3m) reward for information leading to his arrest or capture.
Qari Mohammad Zafar is believed to have been living in South Waziristan where he is said to have been closely involved with Qari Husain - allegedly the Taliban's chief trainer of suicide bombers.
Lashkar-e-Jhangvi was banned in 2001 for its role in fanning sectarian violence. It is also linked with the 2002 murder of US reporter, Daniel Pearl and other militant attacks, particularly in the southern city of Karachi.
The BBC's Syed Shoaib Hasan in Islamabad says that analysts believe many attacks claimed by the Taliban in recent years were in fact carried out by Qari Zafar's Lashkar-e-Jhangvi.
The group is believed to be behind the Punjabi Taliban who are blamed for a series of audacious assaults against top Pakistani military targets in 2009.