Mr Trump tweeted his decision today after departing Washington for a world leader summit in Argentina, where he and Mr Putin were to meet. "I look forward to a meaningful Summit again as soon as this situation is resolved!" he tweeted, apparently from aboard Air Force One. Russian Federation says the ships illegally entered its territorial...
Kiev and Moscow continue to trade barbs, amid accusations of a large-scale Russian invasion of Ukraine.
"Germany is one of our closest allies, and we hope that states within North Atlantic Treaty Organisation are now willing to deploy naval vessels to the Sea of Azov in order to support Ukraine and to guarantee its safety", Bild quotes him as saying.
Following the incident, Ukraine's Navy said Russian Federation had "once again demonstrated its aggressive nature and complete neglect of the norms of worldwide law".
Trump, who was to arrive to arrive in Buenos Aires tonight for two days of diplomacy, threw the meeting into doubt earlier in the week when he told The Washington Post that he might cancel over the conflict with Ukraine.
North Atlantic Treaty Organisation spokeswoman Oana Lungescu responded to Poroshenko's request by saying the military alliance already has a strong presence in the Black Sea region.More news: Ireland's Johnny Sexton wins rugby's world player of year
"Don't believe Putin's lies", Poroshenko told Bild, Germany's biggest-selling paper, comparing Russia's protestations of innocence in the affair to Moscow's 2014 denial that it had soldiers in Crimea even as they moved to annex it.
Lavrov, speaking in Geneva, said Russian border agents and interrogators had found documents on the vessels that "clearly show that these ships had been ordered to not inform the authorities of Kerch Strait and to try and break into the Sea of Azov secretly".
The United States and the European Union have imposed sanctions on Russia over its actions toward Ukraine since 2014, when Moscow annexed Crimea following the toppling of a pro-Russian leader in Kiev.
It has raised fears of a wider escalation - in a conflict that has killed more than 10,000 people since 2014 - and prompted global calls for restraint. Russia has denied supporting the pro-Russian insurgency and has maintained that Crimea voted to join Russia as part of a legitimate referendum.
The Nord Stream 2 project is a potentially serious problem for Ukraine which now earns large transit fees from piping Russian gas to Europe and stands to lose out.
The 24 Ukrainian sailors are now being detained in Crimea and their ships impounded by Russian forces.
He said the summit will also give Trump an opportunity to discuss trade with Chinese President Xi Jinping, and attempt to get some kind of deal to avoid a prolonged trade war.