Left parties are awaiting a response from External Affairs Minister Pranab Mukherjee on their letter -- setting a deadline of July 7 for the United Progressive Alliance government to clarify whether it is going to the International Atomic Energy Agency -- Communist Party of India-Marxist General Secretary Prakash Karat said on Saturday.

"We have sent a letter to Pranab Mukherjee on Friday and we are waiting for his reply," Karat said before meeting CPI-M patriarch Jyoti Basu at his Kolkata residence.

Karat, along with West Bengal Chief Minister Buddhadeb Bhattacharya and CPI-M state Secretary Biman Bose, held a meeting with Basu for over 45 minutes.

They apprised him of the latest developments on the stand-off on the Indo-US civil nuclear agreement, party sources said.

After the meeting, none of the leaders spoke to the press.

On Friday, the Left parties, which have decided to withdraw support the moment the UPA government proceeds to operationalise the Indo-US nuclear deal, set the deadline of July 7 for the ruling coalition to clarify whether it was going to the IAEA.