Senior military officers from more than 30 countries across Europe and beyond met in England on Thursday to flesh out plans for an international peacekeeping force for Ukraine as details of a partial ceasefire are worked out.

U.K. Prime Minister Keir Starmer said he didn’t know whether there would be a peace deal in the Russia-Ukraine war, but “we are making steps in the right direction” as a “coalition of the willing” led by Britain and France moves into an “operational phase.”

“We hope there will be a deal, but what I do know is if there is a deal, the time for planning is now,” he said during a visit to the meeting of military planners at a British base in Northwood, just outside London. “It’s not after a deal is reached.”

“It is vitally important we do that work, because we know one thing for certain which is a deal without anything behind it is something that (Russian President Vladimir) Putin will breach,” he said.

French President Emmanuel Macron said a meeting of the “coalition of the willing” will take place Thursday in Paris in the presence of Ukraine’s President Volodymyr Zelenskyy.

Ukraine and Russia agreed in principle Wednesday to a limited ceasefire after U.S. President Donald Trump spoke with the countries’ leaders this week, though it remained to be seen when it might take effect and what possible targets would be off limits to attack.

Zelenskyy, speaking in Norway on Thursday, said that although he originally had sought a broader ceasefire, he was committed to working with the U.S. to stop arms being directed at power production and civilian facilities.

“I raised this issue with President Trump and said that our side would identify what we consider to be civilian infrastructure,” Zelenskyy said. “I don’t want there to be any misunderstanding about what the sides are agreeing on.”

The tentative deal to partially rein in the three-year war came after Putin rebuffed Trump’s push for a full 30-day ceasefire. The difficulty in getting the combatants to stop targeting one another’s energy infrastructure highlights the challenges Trump will face in trying to fulfill his campaign pledge to quickly end the war.

Negotiators from Moscow and the U.S. will meet Monday in Riyadh, Saudi Arabia, Putin’s foreign affairs adviser Sergei Ushakov told Russian news agencies.

Zelenskyy said team would also meet with the U.S. in Saudi Arabia to discuss technical issues, and then the U.S. will act as an intermediary running “shuttle diplomacy” between Kyiv and Moscow.

Despite the negotiations, hundreds of drone attacks were launched overnight by both sides, injuring several people and damaging buildings.