Nikki Haley, the U.S. ambassador to the United Nations, accused Russia on Monday of taking “outlaw actions” against Ukrainian ships in an incident at sea this weekend and vowed that sanctions punishing Russia’s annexation of Crimea would continue.

Speaking at an emergency meeting of the Security Council called by both Russia and Ukraine, Haley said the United States would welcome a normal relationship with Russia.

“But outlaw actions like this one continue to make that impossible,” she said. “The United States will maintain its Crimea-related sanctions against Russia. Indeed, further Russian escalation of this kind will only make matters worse.”

Haley pointedly noted she had spoken with President Trump and Secretary of State Mike Pompeo before coming to the Security Council. So far, she is the most senior U.S. official to speak publicly on Sunday’s incident.

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She said Russia had acted illegally, and arrogantly, when it blocked three Ukrainian ships traversing the Kerch Strait as they sailed from Odessa on the Black Sea to Mariupol on the Azov Sea. They opened fire on the fleet, injuring six sailors. The ships, and at least 23 sailors, are now in Russian custody.

Despite a bilateral treaty granting both countries the right to use the Azov Sea, Moscow closed the strait to the Ukrainians by positioning a cargo vessel beneath a bridge that it finished building only two months ago.

The maritime confrontation has turned long-simmering tensions between Ukraine and Russia into a full boil. Ukrainian President Petro Poroshenko declared he was implementing martial law for 30 days, which would ban protests and give Poroshenko more latitude in dealing with Moscow.

Ukrainian officials warned Moscow could be preparing more acts of aggression, including a land assault on the Ukrainian port city of Mariupol. Russian officials accused Ukraine of attempting to stir up tensions and stoke conflict.

Dmitry Polyanskiy, Russia’s deputy envoy, said the Ukrainian ships had ignored Russian calls to stop for a customs check made necessary by threats from Ukrainian radicals to blow up the Russian bridge over the Kerch Strait. He said the Ukrainian ships had illegally crossed Russia’s border.

“We consider such steps a violation of Russian sovereignty,” he said, labeling Ukraine’s actions “banditry.”

Ukraine’s ambassador to the U.N., Volodymyr Yelchenko, called Polyanskiy’s account of the incident “an outright lie” and urged the Security Council to tighten sanctions against Russia.

“This is the only way,” he said. “Because Russia doesn’t understand any other language.”

Debate over the incident quickly slid into a broad condemnation of Russia’s actions since it annexed Crimea in 2014 and set off a group of pro-Russian separatists still fighting government forces in eastern Ukraine.

“Sunday’s outrageous violation of sovereign Ukrainian territory is part of a pattern of Russian behavior,” Haley said, citing the conflict that has killed more than 10,000 people in eastern Ukraine.

“What we witnessed this weekend is yet another reckless Russian escalation,” she added.

Jonathan Allen, the deputy chief of Britain’s U.N. mission, said Russia was trying to consolidate its illegal annexation of Crimea by building the bridge linking Crimea and Russia, and forcing Sunday’s confrontation.

“We do not and will not recognize the illegal annexation of the Crimean Peninsula by Russia,” he said. “We continue to fully support Ukraine’s sovereignty and territory.”

But Polyanskiy said Russia's annexation of Crimea is irreversible.

“The issue of who Crimea belongs to, for us and Crimeans, is not an open question anymore,” he said. “Whether you like it or not. No sanctions will change our opinion.”