Indian police have arrested two men in the eastern city of Calcutta suspected of supplying the Mumbai attackers with mobile phone cards.

A police spokesman said the two were being questioned "about procurement of sim cards used in Mumbai, where at least 170 people died in the attacks. Few other details were given of the detentions on Friday night.

India has blamed Pakistan-based militants for the assault on Mumbai, but Islamabad denies any role. The gun and bomb attack last week on multiple targets in India's commercial capital claimed the lives of at least 161 civilians and members of the security forces. Nine of the 10 militants believed to have mounted the attack were also killed and the 10th suspect is in custody.

In a separate development, Pakistani media reported that Pakistan went on high alert during the attacks after a hoax call to President Asif Ali Zardari. A prank caller pretending to be Indian foreign minister Pranab Mukherjee spoke to the Pakistani leader in a threatening manner on 28 November, the Dawn newspaper reports.

Asked by Reuters news agency for comment, a diplomat with knowledge of the exchanges said the report was accurate. Pakistan's air force was placed on "highest alert" for 24 hours as a consequence.

India and Pakistan, which both possess nuclear weapons, have fought several wars since partition in 1947.

Militants arriving by dinghy attacked Mumbai on the night of Wednesday 26 November, targeting two luxury hotels, the main railway station, a hospital, a Jewish centre, a cafe and other sites. Crowds were sprayed with gunfire indiscriminately and hostages at the Jewish centre were shot dead. Those killed included 26 foreigners.

A claim of responsibility was made by a previously unknown Islamic militant group calling itself the Deccan Mujahideen – a reference to a mainly Muslim region of India.

Indian media have named the surviving gunman as Azam Amir Qasab, a Pakistani, and say he has links to a Pakistan-based Kashmiri militant group, Lashkar-e-Taiba. The group denies involvement.

Pakistan's government has strongly denied any involvement in the Mumbai attacks and its foreign minister, Shah Mahmood Qur­eshi, said his country would cooperate with India to "combat terrorism in all its forms and manifestations".

Indian ministers have themselves come under immense public pressure for failing to prevent the attacks and the government has moved to beef up the navy and the air force.

But the new home minister, Palaniappan Chidam-baram, said India would remain a "secular, plural, tolerant and open society" despite the attacks.