Washington DC- US lawmakers have introduced legislation that would bar President Donald Trump's administration from unilaterally annexing, occupying, or otherwise controlling the territory of a NATO ally.

The proposal, put forward by Republican Senator Lisa Murkowski and Democrat Jeanne Shaheen on Tuesday, comes amid Trump's escalating threats to seize Greenland, a Danish territory.

The senators warned that any attempt to seize Greenland would violate the NATO treaty, weaken alliance cohesion and undermine efforts to counter threats from Russia and China.

"NATO remains the most successful defensive alliance in history, and its credibility rests on the shared understanding that member states' sovereignty will be respected and defended by one another," the senators said.

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The bill has poor chances of passing in the Senate and later the House of Representatives.

It would prevent the administration from using funds from the defense or state departments to carry out actions against NATO territory.

A similar bipartisan measure has also been introduced in the House of Representatives, supported by more than 20 lawmakers, though its chances of passing are equally slim. And on Monday, far-right Republican congressman Randy Fine introduced a rivaling measure authorizing Trump "to take whatever steps necessary to annex or acquire Greenland."

Danish Prime Minister Mette Frederiksen and Greenlandic Premier Jens-Frederik Nielsen have repeatedly stressed that Greenland is not for sale and will not be annexed.

Trump has brushed off the warnings and has insisted that the US will take over the island by any means necessary.