'I don't want anyone to think this is fun and games.
"Maybe I won't even have the meeting", Trump told the Washington Post.
Meanwhile, U.S. State Department spokeswoman Heather Nauert urged European states to do more to support Ukraine and said Washington wants to see tougher enforcement of sanctions against Russian Federation.
The number of Russian units deployed along the Ukraine-Russian border has "grown dramatically" while the number of Russian tanks has tripled, Poroshenko said, citing intelligence reports but giving no precise timescale for the buildup. Three hospitalized sailors were also formally detained for two months.
Caravan migrants explore options after Tijuana border clash
He said officials were receiving more requests from migrants wanting to return to their countries, but did not have a number. Most were dispirited after the US agents fired tear gas on the group of migrants trying to cross into the USA on Sunday.
The rest are expected to face trial on Wednesday, she said, while three others were still in hospital after being wounded in the weekend clash.
The move comes days after Russian warships seized several Ukrainian naval vessels, adding to tensions with neighboring Ukraine over the land Russia seized in 2014. "In economic terms we need to decide if we are going to follow the economic globalization and free market or if we are going to choose unilateralism and protectionism".
It is the first time Ukraine has imposed martial law since Russian Federation seized Crimea in March 2014 and backed separatists fighting Kyiv's forces in a war that erupted in the eastern provinces of Donetsk and Luhansk the following month. That fighting has killed at least 10,000 people since 2014 but eased somewhat with a 2015 truce.
President Putin has lashed at Ukraine over its imposition of martial law, depicting it as a cynical pre-election ploy by the country's unpopular president while also mocking western countries over their "short-sighted" support for Kiev.
Russian President Vladimir Putin expressed concern about the decision to impose martial law and told German Chancellor Angela Merkel he hoped Germany could influence Ukraine to avoid any "reckless acts".
Melania Trump Unveils 'American Treasures'-Themed WH Holiday Decor
Topiary trees line the East colonnade during the 2018 Christmas Press Preview at the White House in Washington, Nov. 26, 2018. In the China Room there are three tables recreated from previous state dinners during the Theodore Roosevelt, John F.
"I'm convinced that there was a deliberate provocation by Russian forces in order to provoke Ukraine for more active measures, similar to what they did in Georgia in 2008".
Moscow has accused Kiev of planning Sunday's confrontation as a provocation aimed at drumming up support for Poroshenko ahead of elections next year and convincing Western governments to impose further sanctions on Russian Federation.
Pavlo Klimkin said that the country's forces were more prepared and better equipped than ever before and the government would not let other parts of the country go the way of the Crimean peninsula.
The comments by the top diplomat come as the Russian President blamed his Ukrainian counterpart for Sunday's incident.
On that note, he asked Ukraine's allies to continue to show "solidarity" and make the cost of any Russian blockade unaffordable for the Kremlin.
Russia-Ukraine sea clash in 300 words
In a speech on Tuesday, German Foreign Minister Heiko Maas said Moscow must respect worldwide law and territorial sovereignty. A Reuters witness in Kerch, a Crimean port, said the Ukrainian vessels were being held there on November 26.