As the stand-off over the India-United States nuclear agreement between the Left Front and the United Progressive Alliance government continued, Rashtriya Janata Dal chief Lalu Prasad Yadav on Tuesday met Congress president Sonia Gandhi [Images] in New Delhi.

Prasad refused to talk to journalists waiting outside Gandhi's residence after the short meeting.

The meeting came in the backdrop of reports that the Railway minister was in touch with the Samajwadi Party, for backing the UPA, in case the Left parties withdrew support to the government.

Meanwhile, senior Samajwadi Party leader Amar Singh met Communist Party of India � Marxist leaders Prakash Karat and Sitaram Yechury to explain his party's position on the prevailing political crisis.

The SP's 39 Members of Parliament can play a crucial role in saving the government in the Lok Sabha in case the Left executes its threat of withdrawing support.

Prime Minister Manmohan Singh [Images] on Monday assured the Left parties that he would come back to Parliament before operationalising the deal. But this would be after the government completed all the necessary processes like getting the International Atomic Energy Agency's approval on the safeguards agreement, a waiver from the Nuclear Suppliers Group and an endorsement of the deal from the US Congress.