British is expected to announce a 'significant increase' in troops stationed on Falkland Islands amid fears Argentina could launch a new invasion.
Defence Secretary Michael Fallon confirmed land, sea and air defences were being upgraded in the face of a "very live threat" from the government in Buenos Aires on BBC Radio 4's Today programme.
His comments follow reports Russia is working towards an agreement to lease 12 long-range bombers to Argentina, triggering concerns they could be used to support a fresh attack.
The island has been the subject of a long-running dispute between the UK and Argentina. Argentina refuses to recognise the British sovereignty of the Falklands, which it calls Las Malvinas, despite its inhabitants voting overwhelmingly to remain a British overseas territory in a 2013 referendum.
Mr Fallon, who is due to set out the Government's plans in a Commons statement later on Tuesday, said the deal was unconfirmed but that Britain had to take account of any future possible threat.
"The threat remains. It is a very live threat. We have to respond to it," he said.
"We do need to modernise our defences to ensure that we have sufficient troops there and that the islands are properly defended in terms of air defence and maritime defence.
"The threat, of course, to the islands remains but so does our commitment to being absolutely clear that islanders have the right to remain British and the right to proper protection by our forces.
"It is our general view that the threat has not reduced. Argentina still, sadly, maintains its claim to the islands 30 or more years after the original invasion and the war and we have to respond to that."
In his Christmas message to residents in the Falklands, David Cameron promised 2015 would be a year when "the British Government, again, steadfastly defends the freedom she helped you secure".
The Prime Minister also announced plans for a bronze statue of the former Prime Minister Margaret Thatcher on the island, which was unveiled in January.
A spokesperson for the Ministry of Defence said Mr Fallon would be making a full statement later on Tuesday.