Hectic efforts to resolve the standoff over the Indo-US nuclear deal continued on Friday night with External Affairs Minister Pranab Mukherjee discussing the issue with top Left leaders who clearly told the government that it should not sign the safeguards agreement with the International Atomic Energy Agency.

Hours after the Left parties threatened to break ties with the United Progressive Alliance if nuclear deal is implemented, Communist Party of India-Marxist general secretary Prakash Karat met Mukherjee and discussed the issue in the light of the government's attempts to go ahead with the agreement.

"I explained to him (Mukherjee) the Left parties' stand adopted at our meeting," Karat told reporters after his over hour-long discussions with the external affairs minister who will be out of the country from Saturday for three days before the June 25 meeting of the UPA-Left committee.

"We have asked the government not to proceed further on the IAEA safeguards agreeement," the CPI-M leader said.

After Karat, CPI national secretary D Raja also met Mukherjee and conveyed a similar message.

Earlier in the day, a senior CPI-M leader made it clear that "if the govrernment takes the next step, we will break with them."

Asked whether CPI-M would vote against the government after withdrawal of support, he said, "Once we break, we will be on the other side (opposition)."

To a question whether the Left parties would delink the IAEA safeguards agreement from the 123 agreement with the US and would be satisifed with a public announcement from the government on the issue, Karat shot back, "Are they (government) going to make a public pronouncement?"

Amid these strong statements, Karat expressed the hope that the government will last its full term and that "we are trying to make serious efforts (in this regard)."

Nationalist Congress Party leader Sharad Pawar [Images], whose party is a key constituent of the UPA, met Karat on Friday morning in an attempt to defuse the situation.

He later said the government should listen to what the Left parties are saying and address their "concerns" while deciding on the nuclear deal.