BRUSSELS: Prime Minister Theresa May will update Britain's partners in Brussels on Thursday on her plans to launch talks by March on quitting the EU, and they will settle their arrangements for the negotiations.

May will join an EU summit starting after 12 pm (1100 GMT) to discuss issues from migration to the economy, security and building up defenses against Russia as Donald Trump prepares to enter the White House with an agenda many Europeans fear may dilute the historic U.S. military commitment to protect them from Moscow.

Summit chair Donald Tusk said in a tweet that May will "update" the leaders "on Brexit preparations" before she leaves early in the evening to let the other 27 EU leaders agree their own strategy over dinner.

An aide to May stressed ahead of the meeting that she saw no problem in not being included - rather saw it as a positive - and said the premier was determined to open the two-year window for divorce talks within three months despite doubts raised by a court case that seeks more parliamentary control of the process.

"They are facing up to the reality that the UK is leaving the EU," the aide told reporters. "That means they are going to need to know how they are going to handle the process."

Continental governments have been impatient for May to start a process which they see as being held up by divisions in London on what to ask for in a Brexit which even few of its supporters had thought likely before the shock referendum vote in June.

They will end their dinner debate by issuing a statement saying they are ready to start talks with London and stand by a commitment made in the days after the referendum to negotiate swiftly, to stick together to preserve the Union and to ensure Britain does not retain EU benefits, for instance on trade access, if it shirks obligations, such as accepting EU migrants.

"They stand ready to start negotiations with the UK as soon as the UK has notified " a draft of the statement said.

It went on to detail how the Council of EU leaders would give a negotiating mandate to the EU's executive arm, the European Commission, while ensuring national governments were kept in the loop by officials named by Tusk to sit in on talks run by the commission's negotiator, former French minister Michel Barnier.

One party less than impressed with the plan is former Belgian Prime Minister Guy Verhofstadt, who has been named by the European Parliament as its representative to the process. He told lawmakers on Wednesday that he was not happy to be given only a subsidiary role in the Brexit talks, even though the EU legislature will have to sign off on any final divorce deal.