CAIRO - Egypt's liberal Wafd party, which controls the second biggest opposition bloc in the outgoing parliament, said on Thursday it had withdrawn backing for two seats won in the first round of elections which it said was rigged. Wafd and the biggest opposition group, the Muslim Brotherhood, said they were quitting the election race before run-offs next week after a vote on Sunday they said was marred by ballot box stuffing, thuggery and dirty tricks. "We are not participating in the run-off and the two candidates that have won will have to leave the party and become independent if they wish to continue in the parliament," said Wafik El-Ghetany, who heads the party's election operation. The authorities said voting was fair. The United States, Egypt's ally and a major aid donor, criticised the vote's conduct. Independent Egyptian monitors cited widespread abuse. Wafd, which controlled 12 seats in the last parliament, won just two seats in the first round on the Nov. 28 and was set to contest nine seats in a run-off on Sunday. The Brotherhood, which had a fifth of the seats in parliament, won none in the first round.