In a possible breakthrough in the Mumbai attack probe, two persons, a trader from Srinagar [Images] and another from Kolkata, were arrested for allegedly buying mobile SIM cards on fake IDs, which were used by terrorists during the November 26 siege.

A senior police officer from Jammu and Kashmir [Images] confirmed that the Kolkata Special Task Force had arrested Mukhtar Ahmad Sheikh, a state police constable, in connection with the Mumbai terror attack.

He informed that Sheikh, who was posted in the Crime Branch, had traveled to Delhi [Images] with a sub-inspector to investigate a case. The duo was arrested from the Kashmir House in Chanakyapuri.

While the sub-inspector was released, Sheikh, a resident of Rainawari in Srinagar, was detained for further interrogations, sources said.

"We are still collecting details about Sheikh's involvement and will comment only after the details are available to us," the officer said.

Tauseef Rehman, 26, a resident of Tiljala Road in Kolkata, was arrested from the Howrah Railway station.

The two were today remanded to police custody till December 19 by Chief Metropolitan Magistrate S S Anand.

Public prosecutor S Pathak submitted that Tauseef used to acquire SIM cards using fake identities and those of dead persons.

"Thirteen such SIM cards were bought by Tauseef which were passed on to Sheikh. Some of this cards were used by terrorists involved in the attack in Mumbai," he said.

The two are the first to be arrested after the 60-hour siege ended on November 29, leaving over 200 dead and nearly 300 injured. Mohammed Ajmal Amir Iman was the lone terrorist arrested during the siege while nine others were killed by security forces.

A highly placed police source told rediff.com on Saturday that these two people would provide key information about the terror attacks in Mumbai.

Meanwhile, scare continues to haunt Kolkata as a Mayor Bikash Ranjan Bhattacharyya got a letter, threatening to blow up some landmarks of the city. The police are probing the origin of the letter.

Top police sources earlier this week said intelligence sources had intercepted a telephone conversation in a locality near West Bengal Chief Minister Buddhadeb Bhattacharjee's home on December 1.

The conversation, said sources, was about attacks on Kolkata's Victoria Memorial, Nicco Park and Salt Lake Central Park. Investigations are on.

The police are also worried about the city's links with a Bangladesh-based terror outfit, Yahya.

This outfit provides constant support to all Lashkar-e-Tayiba operations, intelligence sources said.

A massive hunt in the city and its adjoining areas is on to trace the buyers of the SIM cards that were used by the terrorists involved in the Mumbai attacks.

With additional inputs by PTI