New Delhi: An alleged key plotter in the 2008 Mumbai attacks now in Indian police custody had been living in Saudi Arabia for two years and was “talent-spotting” for another “massive attack”, an Indian police official said on Tuesday.

Sayeed Zabiuddin Ansari, also known as Abu Hamza and Abu Jindal, was arrested at Delhi airport on June 21 on his arrival from Saudi Arabia. Police revealed his arrest only on Monday, after interrogating him for five days about the three-day rampage in the financial hub of Mumbai that killed 166 people.

Police said Ansari helped coordinate the attack by 10 members of Pakistan's Lashkar-e-Taiba (LeT) militant group from a “control room” in the Pakistani city of Karachi and also helped to train the gunmen.

Until his arrest, Ansari had been living in Saudi Arabia on a Pakistani passport, an official at New Delhi's anti-terrorist police unit told Reuters on condition of anonymity.

During his stay in the desert kingdom, Ansari sought to recruit volunteers for another Mumbai-style attack, the official said. He would not say where the planned attack was to have taken place or even whether India was the target.

Asked how India had learned of Ansari's whereabouts, the official said: “We had inputs and we acted on them.” He would not elaborate, but some Indian media, quoting sources, said the United States, which has sought to deepen its counter-terrorism relationship with India, had provided the information.

The Hindu newspaper, quoting government sources, said the arrest came after months of painstaking diplomatic talks between Riyadh, Washington and New Delhi. Indian officials had travelled to Saudi Arabia to lobby for him to be handed over, it said.

It was not clear whether Ansari was in Saudi custody before his deportation from the kingdom or even how he had travelled to Delhi. One newspaper said the Saudis had asked India to send a plane to take him home.

The Saudi embassy in Delhi could not be reached for comment.

Indian media, quoting intelligence and police sources, said Ansari had admitted during interrogation to training the attackers, teaching them Hindi and speaking to them by telephone during the attack. He said Hafiz Saeed, the suspected mastermind of the attack and founder of the LeT, was present in the Karachi “control room”, media quoted the sources as saying.

Washington has offered a $10 million reward for information leading to Saeed's arrest.

Ansari's arrest casts a fresh spotlight on Pakistan's history of backing militant groups as a tool of foreign policy.

Pakistan's ISI military intelligence agency nurtured the emergence of the LeT in the early 1990s to serve as a proxy to fight Indian forces in Kashmir.

Pakistan denies backing militant groups, but experts believe the security establishment maintains a relationship with LeT.

Pakistan's government has not commented on Ansari's arrest.

A Gulf-based source familiar with the Ansari case said Pakistan had exerted pressure on Saudi Arabia not to release him into Indian custody. “The ISI wanted Abu Hamza to be handed over to Pakistan rather than anywhere else,” he said.

An Arab diplomat in Islamabad expressed surprise that Saudi Arabia had handed over Ansari to India.

“This makes no sense that the Saudis would help India and anger the Pakistanis. The Saudis see Pakistan as their nuclear guarantee against Iran and they would never go against the ISI,” he said.

India's Foreign Ministry and analysts played down any suggestions that Ansari's arrest could damage diplomatic talks with arch-rival Pakistan on a host of disputed issues.

“This arrest is unlikely to have a negative impact on talks between India and Pakistan unless further investigations reveal that the arrested person was used by Pakistan to plot another terror attack on India,” said B. Raman, a former top Indian intelligence official and now security analyst.

The Mumbai attacks heightened tensions between nuclear-armed India and Pakistan, which have fought three wars since 1947, and have continued to cast a pall over fragile relations ever since.

Ten militants arrived on the Mumbai shoreline in a dinghy on Nov. 26, 2008, before splitting into four groups and embarking on a killing spree. They held off elite commandos for up to 60 hours in two luxury hotels and a Jewish centre in the city. The only attacker to survive was sentenced to death in 2010.

A voice believed to belong to Ansari was recorded talking to the gunmen attacking the Jewish centre. He is reported to have told the attackers to convey to the media that the “attack was a trailer and the entire movie was yet to come.”