Hafiz Saeed at a rally in Lahore, Pakistan
The US has offered a $10m (£6.2m) bounty for Hafiz Mohammad Saeed, the founder of Pakistan-based militant group Lashkar-e-Taiba [LeT].
Saeed now heads the Jamaat-ud-Dawa group, widely seen as a front for LeT - which is blamed for the 2008 Mumbai attacks in India.
A $2m bounty was also announced on Abdul Rehman Makki, Saeed's brother-in-law and co-founder of Lashkar.
Both Jamaat-ud-Dawa and Lashkar-e-Taiba are blacklisted by the US.
The US announced the award for their capture or information leading to their capture, officials said.
The three-day rampage in November 2008 by 10 gunmen in Mumbai left 165 people dead. Nine of the attackers were also killed.
India blamed the Mumbai attacks on LeT, and India-Pakistan ties hit rock bottom.
The sole surviving gunman, Pakistani national Mohammad Ajmal Amir Qasab, was captured and sentenced to death by a court. His appeal is pending.
Saeed figures prominently on a list of "most wanted" given to Pakistan by India. Jamaat-ud-Dawa denies it operates as a front for militancy.
He was held after the Mumbai attacks but released without charge.
The US State Department's Rewards for Justice website describes Saeed as "a Pakistani citizen" with "red hair" and "brown eyes".
"Hafiz Mohammad Saeed is a former professor of Arabic and engineering, as well as the founding member of Jamaat-ud-Dawa, a radical Deobandi Islamist organisation dedicated to installing Islamist rule over parts of India and Pakistan, and its military branch, Lashkar-e-Taiba," the website says.
India welcomed the announcement of the reward.
"It reflects the commitment of India and the United States to bring the perpetrators of the Mumbai terrorist attack to justice and continuing efforts to combat terrorism," the Indian Ministry of External Affairs said in a statement.
"It also sends a strong signal to LeT as also its members and patrons that the international community remains united in combating terrorism," it added.
Interpol has issued an arrest notice against Saeed for his role in the Mumbai attacks and the US has designated LeT and Jamaat-ud-Dawa as "Foreign Terrorist Organisations".
Cables released by Wikileaks in December 2010 attributed to US Secretary of State Hillary Clinton said Hafiz Saeed and Zaki-ur-Rehman Lakhvi, head of Lashkar-e-Taiba, "continue to run" LeT "despite being detained for their role" in the Mumbai attacks.
The message alleged that Mr Lakhvi and Saeed "planned, directed and executed" the group's attacks in South Asia.
Correspondents say Saeed continues to operate in Pakistan, making anti-India speeches and even participating in anti-US rallies in February.