Ukraine’s parliament approved a 30-day presidential martial law decree amid a serious row with Russia, diplomatic sources said on Monday.

The decree imposes martial law in areas of the country seen as most vulnerable to attack from its giant neighbor, Russia, including coastal and border regions.

A total of 276 lawmakers voted to approve the decree, which goes into effect on Nov. 28 and lasts for 30 days.

Russia on Sunday seized three Ukrainian naval ships off Russian-held Crimea in the Sea of Azov.

Russia said the vessels had ignored calls to stop, sparking military action.

Russia intervened as the Ukrainian naval ships were relocating from Odessa to the Port of Mariupol in the Sea of Azov.

The Ukrainian Navy accused Russia of opening fire on its warships, adding that its crew members were wounded and its vessels seized by Russia.

Russia and Ukraine have been at loggerheads since 2014, when Russia annexed Crimea after a controversial referendum.

Turkey, as well as the UN General Assembly, say the annexation was illegal.

Ukraine has also blamed Russia for separatist violence in eastern Ukraine, near the border with Russia.