BRUSSELS (AP) — The European Union's top official said time has come to "inject fresh momentum" into post-Brexit negotiations to try and secure a trade deal between the 27-nation bloc and the departing U.K. before the end of the year.

Speaking ahead of a video-conference with British Prime minister Boris Johnson and other European officials, EU Commission President Ursula von der Leyen said in a Twitter message that the EU is "available 24/7," as both sides remain at loggerheads on various issues on trade.

The EU and Britain disagree notably on regulations for businesses and for the fishing industry in particular, with the U.K. adamantly opposed to EU demands for long-term access to British waters.

Last week, the EU and the U.K. agreed to intensify their negotiations following another inconclusive round of discussions.

The U.K. left the political institutions of the EU on Jan. 31 but remains inside the EU's tariff-free economic zone until the end of the year. This transition period could have been extended by two years but the U.K. made clear last week it would not seek a prolongation.

European Council President Charles Michel and David Sassoli, the president of the European Parliament, will attend Monday's meeting alongside von der Leyen. Britain's Michael Gove, the minister in charge of Brexit preparations, and David Frost, the U.K chief negotiator, are set to assist Johnson.