President Trump on Monday evening spoke by phone with Russian President Vladimir Putin to express his condolences about a terrorist attack in St. Petersburg earlier in the day.

Trump offered Putin the full support of the U.S. government in response to the subway attack. Trump and Putin "agreed that terrorism must be decisively and quickly defeated," according to the White House press secretary's office.

The subway explosion killed 11 people and injured more than 40 others shortly before the city's rush hour. It's unknown who carried out the attack, though it may have been carried out by a suicide bomber who had pledged allegiance to a terrorist group.