NEW DELHI, Oct 6: India's main communist parties on Wednesday opposed any involvement of the FBI in the probe into a Series of blasts that killed 60 people in Assam and Nagaland in the past week.

US Ambassador David Mulford had written to the Assam Chief Minister Tarun Gogoi offering FBI assistance for investigating the recent attacks in Assam. "This action constitutes a gross violation of norms and a direct interference in the internal affairs of the country," the Communist Party of India (Marxist, CPI-M) said in a statement.

There is no mystery about who is responsible for the recent bomb blasts and attacks in Assam, said the CPI-M, which shores up Prime Minister Manmohan Singh's ruling coalition.

"It does not require the FBI to find out who is responsible for the series of attacks in Assam. Such problems in the North East have a political dimension and the US Ambassador's suggestion is an interference in the internal affairs of the country," CPI-M said.

"The US Ambassador has no business to write to a state chief minister directly making such an offer which involves the internal security of the country.