FILE PHOTO: European Commission President Jean-Claude Juncker delivers a speech during a debate at the European Parliament in Strasbourg, France, March 12, 2019. REUTERS/Vincent Kessler

BRUSSELS (Reuters) - European Commission President Jean-Claude Juncker warned British Prime Minister Theresa May against requesting a Brexit delay beyond European Parliament elections due on May 24-26, unless the United Kingdom takes part, an EU spokeswoman said.

Prime Minister Theresa May requested on Wednesday a three-month postponement of the Brexit date to June 30 after failing to get her divorce deal ratified in UK parliament.

A spokeswoman for Juncker said he held a phone call with May earlier on Wednesday ahead of a summit of all EU national leaders in Brussels on Thursday and Friday.

“President Juncker thinks it is good that the PM sets out her thoughts to the leaders ahead of the (EU summit). However, President Juncker has formally warned the PM against including a date for the extension that is after the EP elections,” the spokeswoman said.

“That’s why he repeated to her his advice... that the withdrawal has to be complete before 23 May - otherwise we face institutional difficulties and legal uncertainty. European parliament elections have to be held (in the UK) if the extension date is after 23 May,” she said.