During his visit to the U.K. on Monday, President Donald Trump expressed further frustration with Russian President Vladimir Putin.

Last month, the U.S. leader had set a 50-day deadline for a truce before imposing so-called “secondary sanctions” on countries doing business with Russia, especially those purchasing Russian oil.

President Trump, meeting with Britain’s prime minister in Scotland, called on Russia to stop its attacks in Ukraine in less than two weeks or face new sanctions and tariffs.