WASHINGTON -- US President Donald Trump said Monday he had spoken with Russian President Vladimir Putin following last week's White House meetings with Ukrainian and European leaders.

Trump told reporters that the call with Putin took place after his Aug 18 meetings with Ukrainian President Volodymyr Zelensky and several European leaders in Washington.

He noted that security guarantees for Ukraine have not yet been finalized, suggesting Europe would take the lead while the United States would provide "backup."

"We have not even discussed the specifics of it," Trump said. "Europe is going to give them significant security guarantees, and they should, because they are right there, but we will be involved from the standpoint of backup to help them."

Trump also revealed that during his Aug 15 meeting with Putin in the US state of Alaska, the two leaders discussed reducing their countries' nuclear arsenals once the Ukraine crisis ends.