Ahead of the expected United Progressive Alliance-Left meet on Thursday, Prime Minister Manmohan Singh [Images], Sonia Gandhi [Images], Congress leaders Pranab Mukherjee and A K Antony discussed modalities of a proposed mechanism to address concerns of Left parties on the Indo-US nuclear deal.

The UPA and Left allies are expected to meet on Thursday to concretise the mechanism, which the Left insists, should comprise leaders from both sides.

"The government's decision may be formally told to us at the meeting which is likely tomorrow," Communist Party of India-Marxist leader Sitaram Yechury told reporters here, maintaining that the government should not proceed with operationalising the agreement "till this mechanism or a committee comes out with its findings".

Three of the four Left parties have expressed willingness to join such a mechanism, which could be a committee at the political level. The CPI-M), the Communist Party of India and the Forward Bloc affirmed that they were ready to join such a mechanism if the need arose, but the Revolutionary Socialist Party informed the government that it would take a decision on the matter after discussions.

Asked whether there should be a time-frame for this mechanism to submit its findings, Yechury said, "Yes, there has to be a time-frame."

To a question if the Bharatiya Janata Party should also be part of the proposed committee, Yechury said, "Let them talk to the government. There have been rulings from the Speaker and the Rajya Sabha chairman that a discussion in Parliament cannot be held under rules which entail voting, which was being demanded by the BJP."