After nearly five years of Russian war against Ukraine, tensions are higher after Russian Coast Guard ships on November 25 attacked and then seized three Ukrainian vessels as they tried to cross the Kerch Strait connecting the Black and Azov Sea. "Everybody should have their eyes wide open".
Mr Poroshenko told MPs the martial law introduced in the country would only affect regions bordering Russia, Belarus and Moldova's breakaway republic of Trans-Dniester.
"I hope politicians and the media will act responsibly and appropriately under the current circumstances and will not attack Ukraine with the theses borrowed from Russian propagandists", he said.
Ukraine said that a Russian ship rammed a Ukrainian tugboat; afterward, Russian crews fired on the tugboat and two navy vessels, injuring six sailors, before seizing the ships.
For the US and its allies, the incident highlights the growing tensions around the Black Sea, which is vital to the economies of NATO's southern members but also a place where there is a military mismatch with Russian Federation.
The latest standoff comes after months of rising tensions between Russia and Ukraine, who have been at loggerheads since a pro-Moscow government in Kiev was toppled more than four years ago, touching off Russia's annexation of Ukraine's Crimean Peninsula and the ongoing war in eastern Ukraine involving pro-Russian separatists. So far, the idea of a multinational flotilla hasn't gained traction amid concerns that such a move could antagonize Russian Federation. But he did not say whether or not the USA indicated any support for that.
Poroshenko said his decree only includes those options that mostly relate to military measures, such as human, military, and financial resources, which, in case of the aggressor's invasion, will allow Ukraine to mobilize all of its resources quickly.
When asked whether there would be a North Atlantic Treaty Organisation response, he said, "We constantly assess what more we can do".
The Kremlin spokesman, Dmitry Peskov, added that Ukraine did it so that its president, Petro Poroshenko, could put off elections by imposing martial law because he was not doing very well in polls. During the U.N. Security Council session, Ukraine's ambassador called for increased sanctions on Russian Federation.
In Kiev, Ukraine's parliament also was deliberating on a plan to impose martial law for a period of 60 days, which would keep its military forces at a heightened state of readiness.
The West has condemned Moscow's increasing control over maritime traffic and harassment of commercial vessels in the area.
Mr Stoltenberg said Mr Poroshenko told him over the phone, "the introduction of martial law will not hinder the working of the democratic institutions" in Ukraine.
At a United Nations gathering, Volodymyr Yelchenko, the permanent representative of Ukraine to the United Nations, said Russia's version of events combines fact and fiction, arguing that this was an "act of open military aggression".