The Trinamul Congress on Sunday night formed an alliance with the Congress in West Bengal to fight the Left Front in the Lok Sabha elections in a significant development that gave the UPA one more ally weaning Mamata Banerjee's party away from the BJP-led National Democratic Alliance.

The decision was announced after External Affairs Minister and WBPCC Pranab Mukherjee's [Images] talks with Trinamul  Congress supremo Mamata Banerjee at a guest house in Kolkata and came on a day when UPA's lead party Congress came under intense pressure from allies like the NCP and the Samajwadi party for more seats.

"We (Congress and Trinamul  Congress) will jointly fight the coming Lok Sabha elections in West Bengal against the ruling Left Front," Mukherjee told reporters with Banerjee sitting beside him.

Asked about the number of seats the Congress and TC would contest,  he said "very soon the final details about the seat-sharing arrangement would be announced."

"Our talks were very useful. As we have come to announce the outcome of the discussion, very soon we will declare the final arrangement that we have arrived at," Mukherjee said.        Banerjee said, "We want to take on the CPI(M) together.

The talks were good." West Bengal has 42 parliamentary seats.