China on Tuesday warned it would take countermeasures if the US goes ahead with plans to deploy ground-based missiles in the Asia-Pacific region.
"China will not stand idly by and will be forced to take countermeasures should the US deploy intermediate-range ground-based missiles in this part of the world," said Fu Cong, the director of arms control at the Chinese foreign ministry.
"And we also call on our neighbours, our neighbouring countries, to exercise prudence and not to allow a US deployment of its intermediate-range missiles on (their) territory," he added, naming Australia, Japan and South Korea.
The new Pentagon chief had said that the US was now free to deploy the weapons following its withdrawal Friday from the Intermediate-Range Nuclear Forces (INF) treaty with Russia.
"Yes I would like to," Esper said when asked if the US was considering deploying new medium-range conventional weapons in Asia.
Esper, however, did not specify where the US intended to deploy the weapons.
"We would like to deploy a capability sooner rather than later," Esper told reporters on a plane to Sydney at the start of a week-long tour of Asia.
"I would prefer months... But these things tend to take longer than you expect."
The INF treaty was considered a cornerstone of the global arms control architecture but the United States said the bilateral pact had given other countries -- namely China -- free rein to develop their own long-range missiles.
Under the pact signed in 1987 by then US president Ronald Reagan and Soviet leader Mikhail Gorbachev, Washington and Moscow agreed to limit the use of conventional and nuclear medium-range missiles (with a range of 500-5,000 kilometres, 300-3,000 miles).
But its unravelling had been on the cards for months amid worsening ties between Russia and the US.
The rise of a militarily more assertive China in the region has worried traditional US allies such as Australia and New Zealand, and Beijing's actions in the South China Sea have alarmed neighbours with competing territorial claims to the strategic waterway.
US Defense Secretary Mark Esper had said Washington wants to quickly deploy new intermediate-range missiles in Asia.