Congress chief Sonia Gandhi [Images] on Friday regretted the Left parties' dissociation with the ruling United Progressive Alliance and put on record her appreciation for them.

"Without their support, the UPA could not have been formed and a good deal of what we have achieved would not have been possible," Sonia said in her opening remarks at a meeting of the UPA coordination committee in Delhi.

Thanking the Left parties "who have been with us during these last four years," she said, "unfortunately, we could not carry them with us on the nuclear agreement despite our best efforts. While we regret their withdrawal of support, it is now time to look ahead."

Her appreciation came even though the Left has been spewing venom on the government for its "obsession" with the nuclear deal.

The Left parties ended their over four-year sweet and sour relationship with the UPA after its efforts to dissuade the government from the Indo-US nuclear deal failed.