Theresa May has touched down in Brussels with a message for Donald Trump
The British PM has been angered by security sources in the United States feeding sensitive information to the press after suicide bomber Salman Abedi massacred 22 people at and Ariana Grande concert.
Trump and May will both be at the Nato summit in Brussels, Belgium, on Thursday.
The President and his team is travelled to Europe after a tour of the Middle East before holding tense talks with European Council President Donald Tusk.
Nato has agreed to Mr Trump's request to join the US-led coalition against so-called Islamic State.
Touhcing down in Brussels, Mrs May said: "That attack I think shows why it is important for the international community, including Nato, to do more in our fight against terrorism.
"I am going to be pushing the UK's agenda on burden sharing.
The prime minister also said other nations must be "prepared to take responsibility" under Nato.
Theresa May will tell Nato members they must help to rid the world of Daesh
Sickening images reveal what's left of the Manchester bomb backpack
Wed, May 24, 2017
The remains of the backpack that killed at least 22 people, with more than 60 injured after Salman Abedi detonated a bomb in the Manchester Arena, at 10:30pm Monday, 22 May 2017
Get Quotes on Home Insurance
1 of 8
12-volt battery that was possible power source
I will be making clear to President Trump intelligence shared between law enforcement agencies must remain secure
Speaking about the leaks to the US publications, Mrs May said: "I will be making clear to President Trump intelligence shared between law enforcement agencies must remain secure."
She said the USA is the other half of Britain's "deepest defence and security partnership".
Ms May will also be urging all Nato members to join the fight against ISIS following the abhorrent attack on British families.
Mrs May is expected to say: “A strong, capable and united Nato is at the heart of the security of each and every one of our nations.
“Our unity in responding to common threats is our most potent weapon.
"We must redouble our resolve to meet the threats to our shared society, whether from terrorism or from Russia."
Donald Trump will spend 36hours in Brussels before heading to the G7 summit in Italy
Donald Trump's visit to Brussels has got off to a terrible start with the US leader and the bloc failing to agree on the most troubling issues on the table.
European Council President Donald Tusk said both sides had expressed "different" opinions on climate change, Vladimir Putin's Russia, and global trade.
Tusk said in a televised statement the two leaders agreed on countering militant violence and on relations with Ukraine.British authorities did not say that the investigation had in fact been compromised by the leaks.
Many European cities, including Paris, Berlin and Brussels, have suffered attacks in the last two years, underlining the importance of confidential intelligence cooperation.
Britain routinely shares intelligence with the United States bilaterally, and also as part of the "Five Eyes" network which also includes Australia, Canada and New Zealand.
Trump was widely criticised this month after it emerged he had discussed sensitive Syria-related intelligence, originating from an ally, with Russian officials at a White House meeting. May said at the time Britain would continue to share information with Washington.