According officials and media reports on Tuesday , during a phone call between US President George W. Bush and the Indian Prime Minister Manmohan Singh the latter one explained the difficulty of implementing a bilateral civil-nuclear energy deal amid the domestic political opposition to the pact. The two signed a nuclear agreement in July 2005.

"The Prime Minister (Singh) explained to President Bush that certain difficulties have arisen with respect to the operationalization of the India-US civil nuclear cooperation agreement," said a press release, which was released in Abuja in Nigeria where Singh is on an official visit.

The Indian embassy in Washington also confirmed the phone conversation.

Singh reportedly said that the government fights strong opposition by four communist parties that support the ruling United Progressive Alliance (UPA) in the context of the nuclear pact with the US.

These parties are against India’s close relations with US, believing that the nuclear agreement would have serious implications for India's strategic sovereignty and foreign policy.

The left-wing parties threaten to withdraw their support for the government if the negotiations with the International Atomic Energy Agency for an India-specific safeguards treaty move any further.

Indian media reported that Singh implied in the phone conversation with bush that the Indian government might not be able to continue the negotiations for the nuclear deal due to the communist opposition.

State Department spokesman Tom Casey said the US believes that the deal is a "good one for the United States, for India and for the broader efforts at non-proliferation."

The nuclear agreement between India and US would allow the US to trade fissile materials and technology with India, ending a three-decade ban. The US had outlawed any nuclear trade with India after it first tested an atomic bomb in 1974.