A bloc of Indian left-wing parties announced Tuesday they were pulling out their backing for the country's coalition government in protest against a nuclear energy deal with the United States.

Their decision, however, was not expected to cause the collapse of the Congress-led government of Prime Minister Manmohan Singh, who last week managed to win support from a regional party to avoid the prospect of early elections. Marxist leader Prakash Karat told reporters that the "time has come" for India's leftists to stop propping up the four-year-old coalition in the wake of Singh's decision to push ahead with implementing the controversial pact.

"We have decided to ask the president for an appointment so that we can formally withdraw support tomorrow (Wednesday)," said Karat in New Delhi.

Indian Foreign Minister Pranab Mukherjee said the government would soon convene a special session of parliament, which is in recess until August 11, to seek a vote of confidence.

"As our supporters, the left parties, have decided to withdraw support ... we will seek a vote of confidence in the Lok Sabha (Lower House)," Mukherjee told reporters after conferring by telephone with Singh, who is in Japan for a meeting of the Group of Eight industrialised nations.

But Singh told reporters in Japan that the government of the world's second most populous nation was not in danger.

"I don't think it will affect the stability of our government," he said.

In New Delhi, Congress spokesman Manish Tiwari added that the reshaped coalition "will prove that it has the numbers in the parliament."

Singh and US President George W. Bush in 2005 unveiled the agreement to share civilian nuclear technology -- a deal that when finalised would see India entering the fold of global nuclear commerce after being shut out for decades.

Singh argues the pact is crucial for India's energy security and to sustain high economic growth. The country currently imports more than 70 percent of its energy needs, and needs an overhaul of its decrepit nuclear energy sector.

But the four-party communist and left bloc, who have 59 seats in the 545-member parliament, insist the deal would bind India too closely to the United States, and have threatened repeatedly to force early elections if it moves forward.

They also believe that allowing UN inspections of the country's civil nuclear programme -- as demanded by the Americans -- would harm India's strategic weapons programme.

US officials have been piling pressure on New Delhi to speed up the process of building domestic consensus, warning of an ever narrowing window of opportunity to get the deal through before November 2008 presidential polls.

The latest US warning came on the eve of a meeting between Bush and Singh in Japan on Wednesday from White House spokeswoman Dana Perino, who pointed to the heavy workload and "a limited number of legislative days" for the US Congress.

New Delhi also has to win a waiver from the Nuclear Suppliers Group to conduct atomic commerce and clinch a pact with the International Atomic Energy Agency allowing international inspections of its civilian nuclear reactors.

Singh's administration is seen as unlikely to collapse thanks to a deal struck last week with the regional socialist Samajwadi Party.

"We have 39 MPs and we have some others who have pledged to vote with us, for the government," Samajwadi Party leader Mulayam Singh told reporters.

Political analyst Yashwant Deshmukh said the walk-out by the left-wing parties was now largely symbolic.

"Right now with the support of the Samajwadi Party, it seems the government will last its term and the deal will also go through," he said. Elections are due in May 2009.