European Commission President Jean-Claude Juncker insisted on Tuesday the EU had done "all in our power" to ensure an orderly Brexit, but said the bloc would await British parliamentary approval for a new divorce deal before ratifying it.
Expressing regret that Britain planned to leave the EU on October 31, Juncker said: "At least we can look ourselves in the eyes and say that we have done all in our power to make sure that this departure is orderly."
"We need now to watch events in Westminster very closely. It's not possible, not imaginable that this parliament will ratify the agreement before Westminster will have ratified the agreement," he told the European Parliament in Strasbourg.
British Prime Minister Boris Johnson is desperately trying to secure a break from Brussels that severs many of the island nation's economic and political ties with Europe after 46 years of EU membership.
Lawmakers in Britain, meeting on a Saturday for the first time in 37 years, voted to demand that Johnson delay Brexit while they further consider his newly-agreed EU divorce agreement.
The government's new strategy is to get parliament Tuesday to approve an accompanying package of legislation that needs ratifying for Brexit to take effect.
Britain has been struggling to agree on how to leave the EU ever since narrowly backing Brexit in a 2016 referendum.