British Prime Minister Theresa May arrives for the European Union leaders summit at the European Council on December 14, 2017 in Brussels.

European leaders are meeting on Thursday to decide whether to grant the U.K. an extension to its Brexit due on March 29.

U.K. Prime Minister Theresa May is in Brussels Thursday to seek support from the bloc's 27 leaders for an extension to Brexit date that would mean a departure takes place on June 30th.

At her arrival in the Belgian capital, May said that it is important is that U.K. parliament delivers on the result of the June 2016 referendum. She also said she regretted having to ask for more time for her country to leave the EU.

The move comes after U.K. lawmakers rejected May's Brexit deal with the EU for a second time earlier this month but also rejected the idea of leaving the bloc without a deal.

May requested the extension on Wednesday in a letter to the EU and said she intended to try to put the Brexit deal before Parliament a third time next week. Whether she can do so or not is another matter, as House Speaker John Bercow said the deal would have to have changed significantly in order to justify putting it before MPs a third time.

Meanwhile at the European Council summit on Thursday, EU leaders will have to agree unanimously to a delay. If they don't, the U.K. could exit the bloc abruptly on March 29 with no deal – in other words, the infamous "cliff-edge" scenario where no agreements are in place related to Britain and the EU's future relationship.

"My assumption is that today we will vote 'yes', in principle (on the request for an extension," Mark Rutte, Dutch Prime Minister, said in Brussels.

He also told reporters that he hopes the fast approaching departure date will pressure U.K. lawmakers to approve the deal.

In the meantime, Ireland's Prime Minister described the situation in London as "somewhat chaotic".

On Wednesday, European Council President Donald Tusk signaled a willingness to grant an extension, only if the U.K. Parliament backs May's deal (formally as the "withdrawal agreement'). He also said that "the question remains open as to the duration of such an extension."