A Chinese military plane came within 20 feet (6 metres) of a US air force aircraft and forced it to take evasive manoeuvres to avoid a collision in international airspace over the South China Sea last week, the U.S. military said on Thursday.

The close encounter followed what the United States has called a recent trend of increasingly dangerous behavior by Chinese military aircraft.

The incident, which involved a Chinese Navy J-11 fighter jet and a U.S. air force RC-135 aircraft, took place on Dec. 21, the U.S. military added in a statement.

"The U.S. Indo-Pacific Joint Force is dedicated to a free and open Indo-Pacific region and will continue to fly, sail and operate at sea and in international airspace with due regard for the safety of all vessels and aircraft under international law," the statement added.

In a meeting with his Chinese counterpart in November, U.S. Defense Secretary Lloyd Austin raised the need to improve crisis communications, and also noted what he called dangerous behavior by Chinese military planes.

Australia's defence department said in June that a Chinese fighter aircraft dangerously intercepted an Australian military surveillance plane in the South China Sea region in May

Australia said that the Chinese jet flew very close in front of the RAAF aircraft and released a "bundle of chaff" containing small pieces of aluminium that were ingested into the Australian aircraft's engine.