Indian Prime Minister Manmohan Singh spoke to US President George W Bush and told him about "difficulties" in implementing a bilateral civil-nuclear energy deal amid the domestic political opposition to the pact, officials and media reports said Tuesday. Bush and Singh, who signed the nuclear agreement in July 2005, spoke by telephone on Monday night in a conversation that also covered issues related to the world trade talks, news agency DPA reported. "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 conversation was confirmed by the Indian embassy in Washington on Monday night. Indian media outlets reported that Singh's conversation marked a complete climbdown by the government on the nuclear pact with the US following strong opposition by four communist parties that support the ruling United Progressive Alliance (UPA). The NDTV network reported that Singh's conversation with Bush indicated that his government could not go ahead with the nuclear deal due to political difficulties. The Times of India daily in its report mentioned that Singh also told Bush that his government would not be able to hold talks with the IAEA because of the opposition by the left-wing parties. Meanwhile, 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."