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B.K. Bangash, File, Associated Press
FILE - In this Thursday, Jan. 1, 2015 file photo, Pakistani police officers escort Zaki-ur-Rehman Lakhvi, center, the main suspect of the Mumbai terror attacks in 2008, after his court appearance in Islamabad, Pakistan. A Pakistani lawyer says authorities have released Lakhvi from prison near Islamabad on Friday, April 10, 2015.

ISLAMABAD — The suspected mastermind of the deadly Mumbai attacks in 2008 was released on bail Friday by a Pakistani court — a move likely to further strain relations with India, which has accused Islamabad of turning a blind eye to Islamic militancy.

The release of Zaki-ur-Rehman Lakhvi, who has been held since his arrest in 2009, drew expressions of concern from both India and the United States.

His lawyer, Rizwan Abbasi, called it "a triumph for law and justice."

Lakhvi has been described as the operations chief for Lashkar-e-Taiba, the group blamed for the series of bombings and shootings in the heart of the Mumbai that killed 166 people.

He is one of seven people on trial at the Adiala jail in Rawalpindi in connection with the attacks. Abbasi said the trial is continuing, with a list of more than 150 witnesses, and Lakhvi must attend the next hearing that is scheduled for Wednesday.

His Pakistani passport was earlier handed over to court authorities.

Lakhvi was first granted bail in December and a court ordered his release March 13 after Abbasi filed a complaint that his client was being held unlawfully. But Lakhvi had remained jailed amid mounting pressure on Pakistan to confront extremists more actively. A court on Thursday again ordered his release.

Lashkar-e-Taiba is an Islamic militant group founded by Hafiz Muhammad Saeed, who now heads a charity known as Jamaat-ud-Dawa, or JuD, which denies any links to the armed group.

Lakhvi could not be reached for comment after his release. A Jamaat-ud-Dawa official denied a request Friday for an interview with Lakhvi.

Pakistan has long viewed armed groups such as Lashkar-e-Taiba as allies in its decades-long struggle with India over the disputed region of Kashmir. The group is formally banned in Pakistan, but is widely believed to be protected by the country's powerful intelligence service.

India has repeatedly urged Pakistan to pursue the case more actively. Islamabad faced renewed pressure following the December attack by the Taliban on a school in the Pakistani city of Peshawar that killed nearly 150 people, mainly children.

In expressing his government's "strong concern" about Lakhvi's release, India's External Affairs Ministry spokesman Syed Akbaruddin said: "This has reinforced the perception that Pakistan has a dual policy on dealing with terrorists."

"Those who have carried out attacks or are posing a threat to India are being dealt with differently," he said, adding that the release was "a most negative development insofar as bilateral ties are concerned."

In Washington, State Department spokesman Jeff Rathke said the U.S. was "gravely concerned" about Lakhvi's release and shared its concerns with senior Pakistani officials.

"Pakistan has pledged its cooperation in bringing the perpetrators, financiers, and sponsors of the Mumbai terrorist attacks to justice, and we urge Pakistan to follow through on that commitment to insure justice for the 166 innocent people, including six Americans, who lost their lives," Rathke said.

In India, a lawmaker from the opposition Congress Party, Anand Sharma, said the release "calls into question the sincerity of the Pakistan government."

Pakistan's Foreign Ministry rejected the allegations, saying the case was still being adjudicated.

"It would not be proper to cast aspersions on Pakistan's commitment to countering terrorism at a time when Pakistan has entered a critical stage of defeating the menace of terrorism," spokeswoman Tasnim Aslam said in a statement.

She accused India of "inordinate delay" in helping with the case, saying it had weakened the prosecution. "We respect the judicial process and are confident that it would serve the interest of justice," she said.

Abbasi told The Associated Press that India had failed to provide enough evidence to keep Lakhvi in detention.

The court "considered all the aspects of this matter, and keeping in view the lapses on the part of Indian authorities, keeping in view the lack of evidence, which has not been provided by the Indian authorities ... the court granted bail."

India wants Saeed, the JuD leader, also to be put on trial for the Mumbai attacks, and the U.S. has offered a $10 million reward for information to bring him to justice.

Saeed was detained for a few months in connection with the attacks but was never charged, and he freely travels around Pakistan, making appearances on TV and in public.

Associated Press writers Ashok Sharma in New Delhi and Bradley Klapper in Washington contributed to this report.