Donald Trump has launched a ferocious attack on his NATO allies just hours after America seized a Russian oil tanker in European waters and as the US threatens to invade Greenland.

The President ripped into 'fans' of the post-WWII military alliance with a reminder that 'most weren't paying their bills' - just 2 percent of their GDP on defense, well short of the 5 percent target set last summer at the Hague.

'Until I came along,' Trump wrote on Wednesday morning. 'The USA was, foolishly, paying for them.'

'Russia and China have zero fear of NATO without the United States, and I doubt NATO would be there for us if we really needed them,' he added.

'We will always be there for NATO, even if they won't be there for us. The only nation that China and Russia fear and respect is the DJT-rebuilt USA.' 

The broadside comes as the US, in another show of its military superiority, seized a Russian oil tanker off the north coast of Scotland. Moscow had recently dispatched a submarine to escort the vessel, which was smuggling sanctioned oil from Venezuela.

Europe is on edge after Trump threatened to seize Greenland, a Danish territory, after his capture of Venezuelan dictator Nicolas Maduro in the early hours of Saturday. 

Britain, France and Italy released a statement backing Denmark on Monday after the White House announced the President was exploring plans to take control of Greenland, including buying the land or taking control of its defense. 

The US seized the Russian-flagged oil tanker Bella 1 in the North Atlantic waters between Iceland and Scotland on Wednesday. 

Dramatic footage showed US special forces storming the ship after pursuing it for weeks in an operation inflaming tensions with Moscow.

The Coast Guard also captured a second tanker, the Sophia, in the Caribbean this morning as America strangles the flow of oil from Venezuela to adversaries including Russia, China and Iran. 

Secretary of War Pete Hegseth put the world on notice by saying that the blockade of Venezuelan oil is in full effect, and said no ship is safe anywhere in the world. 

'The United States continues to enforce the blockade against all dark fleet vessels illegally transporting Venezuelan oil to finance illicit activity, stealing from the Venezuelan people,' he wrote on X.