The Kremlin has blamed the United States for an attack on Crimea with a U.S.-supplied missile loaded with a cluster warhead that killed at least four people and injured 151, warning that retaliation would follow.
Russia's special military operation in Ukraine has deepened a crisis in relations between Russia and the West, and Russian officials said the conflict is entering the most dangerous escalation to date. But directly blaming the U.S. for an attack on Crimea is considered as a step further.
At least two children were killed in the attack on Sevastopol on Sunday, Russian officials said. People were shown running from a beach near the city and some of the injured being carried off on sun loungers.
"The involvement of the United States, the direct involvement, as a result of which Russian civilians are killed, cannot be without consequences," Kremlin spokesman Dmitry Peskov said on Monday.
"Time will tell what these will be," he said. "Just ask my colleagues in Europe, and above all in Washington, ask the press secretaries why their governments are killing Russian children."
Kyiv did not comment on the attack but denies targeting civilians.
Moscow has increasingly blasted Washington and Kyiv's Western backers for supplying weapons to be fired on Russian targets, calling them direct participants in the conflict.
Russia's Foreign Ministry summoned U.S. Ambassador Lynne Tracy and told her Washington was "waging a hybrid war against Russia and has actually become a party to the conflict".
"Retaliatory measures will definitely follow," it said.
Tracy said Washington regretted any loss to civilian life, State Department spokesman Matthew Miller told reporters.
Pentagon spokesman Major Charlie Dietz said Ukraine "makes its own targeting decisions and conducts its own military operations".
A U.S. official later said Ukraine was not targeting civilians. It seemed that the Russians were able to intercept an ATACMS missile that was targeting a missile launcher and the missile exploded with shrapnel raining down on the beach, the official added.
Ukrainian President Volodymyr Zelensky said on Monday Ukraine has hit more than 30 Russian oil processing and storage facilities.
The Ukrainian military has stepped up attacks on Russian oil infrastructure this year, seeking to disrupt oil supplies to the Russian army and curb Moscow's revenues to finance the current conflict.
New round of sanctions
Separately, European Union countries adopted a 14th package of sanctions on Russia that aims to close some loopholes and hit Russia's gas exports for the first time, EU foreign ministers said on Monday.
The new restrictions on gas aim to reduce Russia's revenues from liquefied natural gas exports by banning transshipments — transferring cargoes from one ship to another — off EU ports and a clause allowing Sweden and Finland to cancel LNG contracts.
The Kremlin said on Tuesday the sanctions were illegal, calling them a double-edged weapon that would damage those countries that imposed them.