Ukrainian lawmakers on Monday voted to introduce martial law in the border areas with Russia after it seized three Ukrainian navy ships and detained 24 sailors in a key waterway that holds strategic importance for both countries.

It's the first time Ukraine has enacted martial law since the conflict with Russia began in 2014, indicating a major escalation in tensions between the two former Soviet Republics.

The law – which could give the government extraordinary powers over civil society – will start on November 28 and will last 30 days. In Parliament, 276 members voted for the motion.

In a statement on Twitter, Ukraine President Petro Poroshenko said martial law would be introduced only in regions bordering Russia, or adjacent to regions where Russian troops are posted. That includes regions bordering the Azov and Black Seas and a portion of the border with Moldova's Transnistria region, where Russian troops are stationed.

“This is where the blow can be struck,” Poroshenko said.

The Ukrainian government's introduction of martial law follows a confrontation with Russia Sunday around a waterway linking the Azov Sea and the Black Sea.

Ukraine said two of its small gunboats and one tugboat were attacked by Russian naval forces Sunday after entering the Kerch Strait en route to the city of Mariupol.

Video of the incident released by Ukrainian officials appeared to show a Russian ship ramming the Ukrainian tugboat.

The incident provoked fury in Kiev, while Russia accused Ukraine of acting as the aggressor, calling the incident a “dangerous provocation” by Kiev.

During an emergency UN Security Council meeting to defuse rising tensions after Sunday's confrontation, US Ambassador Nikki Haley called the incident “yet another reckless Russian escalation” and demanded that the Kremlin release the sailors.
“This is no way for a law-abiding, civilized nation to act,” Haley said, adding that it was an “outrageous violation” of Ukraine's sovereignty.

“Impeding Ukraine's lawful transit through the Kerch Strait is a violation under international law. It is an arrogant act that the international community must condemn and will never accept.”

Secretary of State Mike Pompeo on Monday called for restraint by Ukraine and Russia following the incident.

“The United States condemns this aggressive Russian action. We call on Russia to return to Ukraine its vessels and detained crew members, and to respect Ukraine's sovereignty and territorial integrity within its internationally recognized borders, extending to its territorial waters,” he said in a statement.

Ukraine's navy said six of its sailors were injured in the incident on Sunday. It added that the tugboat and one of the gunboats were disabled and towed away by the Russian navy. The other gunboat was undamaged but was also seized by Russia, Ukraine said.

On Monday, Russia's state news agency RIA reported that all 24 sailors aboard the three boats were detained by Russia, citing sources in Crimea's security agencies. Three of the sailors were now in a hospital, it added.

The Kerch Strait — a shallow, narrow stretch of water just 2 to 3 miles wide at one point — connects the Azov Sea with the Black Sea and runs between the Crimean Peninsula and Russia. It is an important economic lifeline for Ukraine, as it allows its ships to access the Black Sea.

It's also the closest point of access for Russia to Crimea, a peninsula Moscow annexed from Ukraine in 2014. A Russian-built bridge over the Kerch Strait was opened in May.