The White House said on Saturday there would be repercussions for U.S.-Pakistan relations unless Islamabad took action to detain and charge Hafiz Saeed.
A Pakistani court ordered the release on Wednesday of Jamaat-ud-Dawa chief Hafiz Saeed, who was put under house arrest in January, and is accused by India and the US of orchestrating the 2008 Mumbai attack that killed 166 people.
The White House on Saturday urged Pakistan to arrest Saeed, calling for him to be prosecuted over the attack.
This is the first time the United States has acknowledged that the recent decision could have an impact on relations between the two countries, who are allies but view each other with suspicion.
Saeed has repeatedly denied involvement in the Mumbai attack.
The violence brought nuclear-armed neighbors Pakistan and India to the brink of war.
The United States had offered a $10 million bounty for information leading to the arrest and conviction of Saeed. India and the US it is a front for the Pakistan-based Lashkar-e-Taiba (LeT) militant group.
The White House said Pakistan’s failure to charge Saeed sent a “a deeply troubling message about Pakistan’s commitment to (combating) international terrorism.” It added that it also was counter to Pakistan’s claim that it did not provide sanctuary to militants.
President Donald Trump has accused Pakistan of harboring “agents of chaos” and providing safe havens to militant groups waging an insurgency against a U.S.-backed government in Kabul.
Pakistan argues that it has done a great deal to help the United States in tracking down terrorists.