A Pakistani court on Friday released on bail the suspected mastermind behind the 2008 attacks in Mumbai, India, that killed 166 people and further strained relations between the nuclear-armed neighbors.

Zaki-ur-Rehman Lakhvi, said to be the operations chief for Lashkar-e-Taiba, the armed group accused of the attacks, was released from prison early Friday morning, according to his attorney Rizwan Abbasi.

During the Mumbai attacks, 10 gunmen infiltrated the city by boat and spent three days spraying bullets and throwing grenades around city landmarks, including two five-star hotels, a railway station and a Jewish community center.

Lakhvi was arrested in Pakistan in 2009 in connection with the attacks. Relations between India and Pakistan, which have fought three wars since independence from Britain in 1947, nosedived after the assault and have not fully recovered.

While Abbasi hailed Lakhvi’s release as "a triumph for law and justice," criticism from India was swift.

"The fact is that known terrorists not being effectively prosecuted constitutes a real security threat for India and the world," said Syed Akbaruddin, spokesman for India's Ministry for External Affairs. "This also erodes the value of assurances repeatedly conveyed to us with regard to cross-border terrorism."

Lakhvi still faces terrorism charges over the Mumbai attacks, but seven years on he has still not been made to stand trial. His lawyers said that bail was granted because of insufficient evidence. Much of the case against Lakhvi is based on the confession of the sole surviving attacker, who was executed in November 2012. Nine other gunmen were killed during the attacks.

Lakhvi was initially granted bail by an Anti-Terrorism Court in Islamabad on Dec. 18, just two days after an attack by the Pakistani Taliban on a high school in the Pakistani city of Peshawar killed 132 children. He was detained again later in December, after public outcry over his release and the school attack, with authorities citing “Maintenance of Public Order” legislation, Reuters reported.

New Delhi expressed anger over his temporary release at the time.

“Pakistan needs to show more seriousness” in taking the trial to its “logical conclusion,” Indian officials said in a statement at the time.

Al Jazeera and wire services