Secretary of State Marco Rubio said Wednesday that an expected minerals deal would give the United States a "vested interest" in Ukraine's security, although he stopped short again of promising formal guarantees.
"I wouldn't couch it as a security guarantee, but certainly, if the United States has a vested economic interest that's generating revenue for our people as well as for the people of Ukraine, we'd have a vested interest in protecting it," Rubio told reporters on a refuelling stop in Ireland.
"Certainly one of the things that provides for Ukraine's long-term prosperity and security is vibrant economic growth and development," eh said.
A growing economy "gives them a tremendous amount of leverage and power and the ability to fund their own defences," he said.
Ukrainian officials agreed in talks with Rubio and President Donald Trump's national security advisor Mike Waltz in Jeddah on Tuesday to back a 30-day ceasefire.
The two sides also agreed to sign as soon as possible a minerals deal giving the United States access to Ukraine's natural wealth.
The deal went unsigned after a disastrous White House meeting on February 28 between Trump and President Volodymyr Zelensky.
Rubio said that the United States was initiating contact with Russia on Wednesday and was gauging its response.
"That's what we want to know -- if they're prepared to do it unconditionally," Rubio said of the Russian response.
"If the response is, 'yes', then we know we've made real progress, and there's a real chance of peace. If their response is 'no', it would be highly unfortunate, and it'll make their intentions clear."
Trump has sharply shifted the US stance by negotiating with Russia and demanding concessions from Ukraine, stunning European allies.
Rubio said Europeans would have to be involved eventually in discussions if they progress as Russia will be keen to end European sanctions.