President Donald Trump arrived at NATO headquarters here Thursday facing renewed questions about the security of intelligence shared with the United States.
Trump is due to face European leaders, including British Prime Minister Theresa May, for the first time since this week's suicide attack in Manchester.
British officials are fuming that information about the attack have surfaced in US media after it was shared with their American counterparts. May plans to "make clear" to Trump on Thursday that information shared between the two countries must remain secure.
"The British police have been very clear that they want to control the flow of information in order to protect operational integrity, the element of surprise," Britain's Home Secretary Amber Rudd told BBC Radio 4's "Today" program. "So it is irritating if it gets released from other sources, and I have been very clear with our friends that that should not happen again."
British media reported Thursday the confrontation over leaks had led to a suspension of intelligence sharing between the Greater Manchester Police and US officials. The BBC and the Guardian newspaper indicated the suspension is temporary and only refers to the Manchester attack, not the entirety of national intelligence.
The intelligence row threatened to dampen Trump's formal introduction to leaders at NATO, the first gathering of heads-of-state that Trump has attended since taking office. While here, he's set to participate in a ceremony honoring NATO's mutual defense pact and meet for talks over dinner.
Trump has met most of the leaders during visits to the White House, but his appearance in Brussels offers the first opportunity for him to hold broader discussions with his counterparts.
For months, Trump has been railing against leaks from inside the US government. It could be a moment for Trump to make a similar case on the world stage.
Administration officials were weighing how Trump would respond when he arrives at the NATO summit Thursday afternoon. The White House had no immediate comment.
Fighting extremism has been a central theme of Trump's first trip abroad. The Manchester terror attack has added urgency to the President's argument.
"When you see something like what happened a few days ago, you realize how important it is to win this fight," Trump said Wednesday night at the Royal Palace here. "We will win this fight. It's a horrible situation, what took place is horrible. Unthinkable. But we will win."
It's the second time this month that Trump's administration has faced questions about the sanctity of intelligence shared by foreign governments.
In a meeting with Russian officials on May 10, Trump revealed highly classified details about a plane bombing plot. The information was gleaned from the Israeli intelligence services, and was said to be so detailed that its origin would be obvious.
Visiting Israel earlier this week, Trump insisted during an off-script moment that he never mentioned Israel by name with his Russian guests. But neither he nor the White House have disputed that he discussed the airliner plot with the Russian foreign minister and ambassador in Washington.
After Trump departed Jerusalem on Tuesday, Israeli Defense Minister Avigdor Liberman said the two governments had discussed the matter and made a "pointed correction."
"Everything we needed to discuss was discussed," Liberman said. "We did an inquiry. Everything that should have been done -- all the conclusions -- everything was done."
Israel's Prime Minister Benjamin Netanyahu said alongside Trump that intelligence coordination between his government and the United States was "terrific."