Asserting there was no going back on the Left's opposition to the Indo-US nuclear deal despite its support to the United Progressive Alliance government, the Communist Party of India-Marxist on Sunday said the onus of running the coalition is on the Congress.

"You should ask the Congress party whether they want to run the government," Karat told reporters when asked about the possible fallout of the Left-UPA stand-off on the issue.

"We are all aware that the Prime Minister (Manmohan Singh [Images]) is very sensitive on the government's relations with the US. But this is not a matter of sensitivity alone. This is an issue of serious import," he said about Dr Singh's challenge to the Left to withdraw support to his government.

The UPA should consider the fact that it is running the government with the support of the Left, Karat said adding, the Common Minimum Programme of the ruling alliance did not say a word about the strategic alliance with the US.

"It is the responsibility of the Congress to see that the government does not take any policy which contradicts with the CMP," he said.

Any discussion or debate in Parliament would show that the government did not have a majority in support of the nuclear deal and the government should heed that message of Parliament, he said.

"Any debate or discussion in Parliament would show that the government is not in majority in Parliament," he said.

Asked about his earlier statement that the government would have to pay a heavy political price if it went ahead with the nuclear deal, Karat said what he had said was that the government would have to face heavy political consequences.