Martial law was imposed in Ukraine for 30 days as president Petro Poroshenko warned of the "extremely serious" threat of a Russian land invasion.

The parliament voted in favour of the measure on Monday night in response to the capture of three Ukrainian navy vessels and twenty-three crew members by Russian ships near the Kerch Strait.

Russia's actions were also condemned at emergency meeting of the United Nations Security Council, where US representative Nikki Haley described the incident as an "outrageous violation of sovereign Ukrainian territory."

The secretary-general of Nato, Jens Stoltenberg, also said there was "no justification" for the seizure of the Ukrainian ships and sailors.

Meanwhile there there violent protests in Kiev and demonstrations outside Russian embassies across the world, including in London, Washington DC and Brussels.