Theresa May will attend what could be her last European Union leaders' summit before formally triggering Brexit under Article 50.
The Prime Minister will attend the first day of the European Council summit in Brussels on Thursday for talks on migration, security and economic growth.
But she will leave on Thursday night, allowing the other 27 leaders to use Friday's informal meeting to discuss the next summit in Rome on March 25, which will celebrate the EU's 60th anniversary.
Mrs May has promised to trigger Article 50 by the end of the month and despite defeats in the House of Lords over the plan, she expects to be able to stick to her timetable.
A Government source suggested the PM would not be attending the Rome summit, which would make this week's European Council her last before Brexit negotiations with the EU are expected to begin.
On the Rome summit, the source said: "We've chosen a different path, we're leaving the European Union and we wish them well."
In Brussels, the PM is not expected to discuss Brexit and has no bilateral meetings arranged with other leaders, but will stress that the UK is a strong advocate of the EU's free trade agenda, and wants to see strong economic growth in the bloc.
She also faces a diplomatic headache over the Polish prime minister's bid to oust European Council president Donald Tusk in a vote at the start of the summit.
Along with other EU leaders, Mrs May has been sent a letter from Polish PM Beata Szydlo, accusing her countryman Mr Tusk of interfering in domestic politics.
Mr Tusk, whose initial two-and-a-half-year term in office expires at the end of May, would be expected to play a key role in the Brexit negotiations and he believes he has the support of many EU leaders to continue.
But the bitter row between former Polish prime minister Mr Tusk and Ms Szydlo's Law and Justice party has led to Warsaw proposing a challenger for the job - Polish MEP Jacek Saryusz-Wolski.
The dispute will come to a head at the summit, when EU leaders will vote on whether Mr Tusk should continue in the role until November 30 2019.
The dispute could have major implications for Mrs May, who needs to forge alliances with European leaders in her negotiations for a Brexit deal after she triggers Article 50 this month.
The president is elected by the European Council by a qualified majority, which means that no single country can veto it.
On Wednesday, Mrs May's official spokesman said the PM would not reveal her voting intention before the summit, adding at a regular Westminster briefing: "The Prime Minister has been clear that she thinks that he (Mr Tusk) is doing a good job."
Elsewhere at the summit, Mrs May will call for more action to counter "Russian disinformation" and "raise the visibility" of Western commitment in the Western Balkans, where Moscow faces allegations of helping to plot a coup attempt in Montenegro.
She is also expected to push EU leaders for "immediate action" to deal with an expected rise in refugees and migrants making dangerous journeys to Europe across the Mediterranean as the weather improves.
Mrs May will encourage the 27 countries to step up the dismantling of people smuggling rings, and suggest they maintain a national safe country of origin list to allow fast-track returns of asylum seekers to the safe nations which should be processing their claims.