Russia's Foreign Ministry summoned senior U.S. diplomats on Friday to protest against remarks by White House national security adviser Jake Sullivan, whom it accused of "effectively endorsing strikes" on Crimea.

"It is time for Washington to learn that any form of aggression against Russia will continue to be met with the strongest possible response," the ministry said.

It did not specify which comments it objected to, but when Sullivan was asked in a CNN interview on Sunday whether Ukraine should have weapons that can reach Russian targets in Crimea, he replied: "Yes. We have not placed limitations on Ukraine being able to strike on its territory within its internationally recognized borders."