WASHINGTON -- US President Donald Trump said Wednesday he is doubting whether NATO would come to US defense when it is needed.

Trump made the remarks two days after Danish Prime Minister Mette Frederiksen warned that a US attack on Greenland could effectively end the military alliance established since the end of the Second World War.

"We will always be there for NATO, even if they won't be there for us," Trump wrote on Truth Social.

Trump and his team are weighing "a range of options" to acquire Denmark's Greenland, including "utilizing the US military," White House Press Secretary Karoline Leavitt told Xinhua in an emailed statement on Tuesday.

Denmark is a member of both NATO and the European Union.