Experts from India’s Defence Research Development Organisation have also watched two live launches of missiles used in the shield system.

The development highlights the fast-changing nature of the strategic engagement between Washington and New Delhi, after decades of frosty relations.

“India is a partner of ours, and we want to provide it with whatever it needs to protect itself,” one US embassy official said. “This fits into the overall strategic partnership we are building.”

Pakistan said on Wednesday night it “will have to take counter-measures to respond” to any agreement between the US and India over a missile defence system.

“No anti-missile and anti-nuclear shield is completely foolproof,” said a senior Pakistani official with detailed knowledge of the country’s own nuclear programme.

“You must consider the fact that the flying time of a missile from Pakistan to India would be hardly a few minutes. Does that give sufficient time to a system like the Patriot to respond? I believe not.”

However, India’s politicians and defence planners have yet to take a final decision on whether to buy any foreign shield systems as they undertake an expensive modernisation of the army and replace ageing Soviet-era military hardware.

“I get the impression the scientists are quite interested, and that some in the strategic policy community . . . see this as a future tool in their kit bag,” another US official said. “But India’s political leadership and its strategic community need to decide what their interests and threats are.”

Satish Nambiar, former head of a military think-tank, said acquiring missile shield technology from Washington would be a sensitive move for any Indian administration.

“It would have very serious political repercussions here,” he said.

New Delhi also views China – with which it has an outstanding border dispute – as a potential adversary, although relations between the aspiring Asian superpowers remain polite.

India has been working to develop its own indigenous missile defence systems, and has conducted two missile intercept tests in the last two years.