Theresa May will promise that UK efforts to tackle Europe's migrant crisis will continue after Brexit as she attempts to build alliances ahead of divorce talks with Brussels.
The Prime Minister will promise that the UK will remain a "reliable partner" and will use one-to-one talks with fellow leaders to insist she wants a "new, positive and constructive" relationship with the EU after Brexit, said Downing Street.
But she will also tell her counterparts that they must boost defence spending following her talks with Donald Trump on Washington's attitude towards Nato.
Mrs May is expected to use the gathering in Malta's capital Valletta to hold one-to-one talks with a series of EU leaders.
This will be her first chance to discuss Brexit face-to-face since she set out her plans and MPs began considering the Bill allowing her to trigger Article 50.
She is expected to underline her belief in a "strong" EU, arguing that it is in the interests of the UK and wider world for the bloc to succeed.
Legislation being fast-tracked through Parliament is aimed at giving Mrs May permission to begin the formal process of Brexit by the end of March.
The main focus of the leaders gathered in Valletta will be measures to tackle the ongoing migrant crisis in the Mediterranean.
Downing Street said Mrs May, who was involved in efforts to address the problem as home secretary, will stress that it remains a big issue for her.
"During the discussions the Prime Minister will stress that migration has been one of her political priorities during her time in Government - and remains so," a spokesman said.
Mrs May will pledge her commitment to the "long-term" challenge both before Brexit and afterwards.
Her aims involve trying to prevent migrants heading to Europe in the first place by supporting refugees close to the homes they have been forced to flee and deterring economic migrants from attempting the dangerous crossing.
Mrs May's approach also involves returning those who arrive in Europe with no right to remain.
The Prime Minister, who last week became the first foreign leader to meet Mr Trump since he entered the White House, will update European leaders on his views on Nato.
Mrs May said she had secured confirmation that Mr Trump was "100% behind Nato" as she appeared alongside the president in the White House.
Mr Trump's criticism of the alliance in the past has alarmed Europe, and some on the continent also have deep concerns about the controversial tycoon's policies.
But Mrs May will say Mr Trump's comments to her about Nato underline the importance of defence and security cooperation.
She will also deliver the message that Nato members need to step up their spending on defence.
The UK and US are among a handful of Nato members to meet the pledge of spending 2% of GDP on defence.
Downing Street said the Prime Minister will use the gathering to tell her counterparts they need to deliver on their commitments so the "burden is more fairly shared".
The Prime Minister is only expected to attend the first part of the summit in Malta, with leaders of the other 27 EU nations continuing their talks on Friday afternoon without her as they consider Brexit and the future of the bloc.