Ukraine's parliament voted on Monday to impose martial law for 30 days, one day after tensions rose as Russia allegedly fired at three Ukrainian naval vessels near Russia-occupied Crimea.
The Ukrainian ships, along with their crews, were seized by Russian coast guard ships.
Ukraine's navy said six sailors were wounded after Russian coast guards opened fire on the three Ukrainian ships near the Kerch Strait — the only outlet for Ukrainian vessels to the Black Sea — and then seized them. Ukraine is demanding the release of the ships and crewmen.
Monday's vote supported President Petro Poroshenko's motion.
Martial law in the country is set to include a partial mobilization and strengthening of the country's air defense. The measures before parliament also included vaguely worded steps such as "strengthening" anti-terrorism measures and "information security."
Speaking at an emergency meeting of the United Nations Security Council on Monday, U.S. Ambassador to the U.N. Nikki Haley called Russia's reported actions an “outrageous violation of sovereign Ukrainian territory,” saying they marked “yet another reckless Russian escalation.”
"[It's] an arrogant act that the international community must condemn," she added. "The United States will continue to stand with the people of Ukraine."
Russian Foreign Minister Sergey Lavrov, however, said Ukraine violated international law and provoked Russia by sending its navy vessels through the Kerch Strait without permission — a claim Ukraine's Ambassador to the U.N. Volodymyr Yelchenko called an "outright lie."
Ukraine and Russia have been locked in a stalemate since Moscow annexed Crimea in 2014.
NATO said Secretary-General Jens Stoltenberg expressed the U.S.-led military alliance’s “full support for Ukraine’s territorial integrity and sovereignty, including its full navigational rights in its territorial waters under international law.”
The incident came after months of incidents in the Sea of Azov that involved inspections and seizures of ships. While a 2003 treaty designates the Kerch Strait and Sea of Azov as shared territorial waters, Russia has sought to assert greater control over the passage since the annexation of Crimea.
Fox News' Lucia Suarez Sang and The Associated Press contributed to this report.