US President George W. Bush telephoned Indian Prime Minister Manmohan Singh Thursday to discuss joint efforts to forge ahead on their countries' controversial nuclear deal, the White House said.

"Both leaders expressed their desire to see the US-India civil nuclear issue move forward as expeditiously as possible," US National Security Council spokesman Gordon Johndroe said in a statement.

The allies have ramped up a diplomatic campaign to secure the international clearances needed for their civilian nuclear cooperation agreement, inked in 2005, which both sides say is key to broadening US-India relations.

Bush told Singh "he looks forward to continuing to work with his government to strengthen the United States India strategic relationship," Johndroe said, adding that they had also discussed stalled World Trade Organizations talks.

Bush and Singh "discussed the importance of all leading WTO Members making contributions to a breakthrough that will put the Doha Round negotiations on a path to conclude an ambitious agreement before the end of the year," he said.

The telephone conversation came ahead of Bush's White House talks on Monday with Prime Minister Yousuf Raza Gilani of Pakistan, India's neighbor and nuclear rival.

India said Thursday it was sending out envoys to lobby for the final international clearances, a diplomatic offensive coming after the ruling coalition survived a hard-fought confidence vote in parliament sparked by left-wing and communist opposition to the pact.

Government officials told AFP that senior cabinet ministers and foreign ministry officials had left New Delhi to solicit the support of members of the International Atomic Energy Agency (IAEA) and the Nuclear Suppliers Group (NSG).

Science Minister Kapil Sibal is travelling to IAEA headquarters in Vienna while foreign secretary Shiv Shankar Menon is in Germany to persuade Berlin, a member of the influential NSG that regulates nuclear commerce, to back the pact.

The NSG groups 45 countries that export nuclear fuel and technology whose rules ban trade with states, like India, that have not signed the nuclear Non-Proliferation Treaty (NPT).

Another senior government envoy, Shyam Saran, was in Ireland, another NSG member, while National Security Adviser M.K. Narayanan will head abroad this weekend, with his schedule not yet fixed, officials said.

Singh, who risked his government to push through the deal, "is now putting in all efforts to get the processes through to get the pact operational," said a senior Indian government official.

The US State Department has said that top US diplomats have been reaching out to their counterparts at the IAEA over the required "Safeguards Agreement" and opening up key Indian civilian nuclear reactors to UN inspections.

The United States is thought to be pressuring Pakistan not to oppose the accord.

In addition, India must obtain a waiver from the NSG, a group of 45 states

Finally, lawmakers in both countries must sign off on the accord.