Iran’s supreme leader sent his foreign minister to Moscow on Monday to ask Vladimir Putin for more help from Russia after the biggest U.S. military action against the Islamic Republic since the 1979 revolution over the weekend.

Donald Trump and Israel have publicly speculated about killing Supreme Leader Ayatollah Ali Khamenei and about regime change, a step Russia fears could further destabilize the Middle East.

While Putin has condemned the Israeli strikes, he has yet to comment on the U.S. attacks on Iranian nuclear sites though he last week called for calm and offered Moscow’s services as a mediator over the nuclear programme.