Vladimir Putin on Monday ordered a barrage of rocket attacks against Kyiv and nine other Ukrainian cities, an action the Russian president himself characterized as a “harsh” response to an explosion on a crucial bridge linking Russia to the occupied Crimean peninsula.

The White House condemned the attacks, which killed at least 11 people, saying they had no military purpose and demonstrated “the utter brutality of Mr. Putin’s illegal war on the Ukrainian people.”

“These attacks only further reinforce our commitment to stand with the people of Ukraine for as long as it takes,” President Biden said in the statement.

The escalation comes as the U.S., allies and security experts have raised the alarm about the prospect of nuclear confrontation to its most dangerous point since the Cold War. 

Experts characterized the overnight missile attacks as a brutal but somewhat predictable response by Putin to the bridge attack, and one that was less risky than the use of a tactical nuclear weapons that he has threatened.

“The easiest, fastest way for [Putin] to strike back is to use missile strikes on civilians, so that’s what he did today,” said Melinda Haring, deputy director of the Eurasia Center at the Atlantic Council. “That doesn’t mean he doesn’t use nukes, but he loses a lot if he uses nuclear weapons.”

The Russian president retaliated after an explosion on Saturday damaged the Kerch Bridge, a Russian rail and road line to Crimea, which Russia annexed from Ukraine in 2014. Putin had celebrated its opening in 2018, and it is viewed as a key supply route for Russia’s military offensive on the south of Ukraine.