Russian state television on Monday aired images of Ukrainian sailors held by Moscow after it seized three of Kiev's ships in a confrontation at sea on the weekend.

 

Russian forces boarded and captured the ships on Sunday, with Moscow accusing the vessels of illegally entering Russian waters off the coast of Crimea in the Kerch Strait despite warnings from a border guard ship.

 

Ukraine and its Western allies say Russia illegally blocked the strait and acted against international law by grabbing the vessels and sailors. They demand Moscow release them.

 

Russia's state-run channel Rossiya 24 showed images of several of the sailors during interrogations by Moscow's security services.

 

At one point, one of the sailors is heard saying "the actions of the Ukrainian armed vessels in the Kerch Strait had a provocatory character" -- parroting the version of events put forward by Russian authorities.

 

One of the sailors appeared to be reading his statement.

 

Ukraine's military was on high alert and its parliament late Monday approved a request by President Petro Poroshenko to impose martial law.

 

Poroshenko accused Moscow of a "new phase of aggression" in a conflict that has dragged out since 2014, when pro-Russian rebels and Russian forces seized territory in Ukraine's east and annexed Crimea.

 

The sea incident has raised fears of a wider military escalation.

 

The UN Security Council met in an emergency session, where U.S. Ambassador Nikki Haley warned Russia against "outlaw actions."