TOKYO/HONG KONG • Both Japan and the United States have complained about separate incidents involving the Chinese military in the East China Sea.

Japan said it scrambled fighter jets after a Chinese vessel sailing in disputed waters launched a drone on Thursday, the latest bout of tension in a longstanding territorial row. The two countries are at odds over a group of small uninhabited islands in the East China Sea, administered as the Senkakus by Japan but claimed as the Diaoyus by China.

Separately, the US Air Force said two Chinese Sukhoi SU-30 fighter jets intercepted an American military aircraft over the East China Sea on Tuesday. The US opposes China's territorial claims in the region and routinely asserts its right to sail or fly in areas it considers international sea or airspace.

Reacting to the drone, Japan dispatched four planes, including two F-15 fighter jets and an airborne warning and control system plane, to waters surrounding the islets, Japan's Defence Ministry said.

Mr Yoshihide Suga, Japan's top government spokesman, said: "This is the first time we see what appears to be a drone flown by Chinese ships that are sailing within territorial waters. This is a new form of activity by China.

"We strictly protest that this is a unilateral escalation and that we absolutely cannot accept it," he said.

Coast guard ships from the two nations routinely patrol the area, known for rich fishing grounds and possible energy reserves, to back their claims.

DRONE ACTIVITY This is the first time we see what appears to be a drone flown by Chinese ships that are sailing within territorial waters. This is a new form of activity by China. MR YOSHIHIDE SUGA, Japan's top government spokesman

The countries have also occasionally engaged in potentially dangerous encounters in the air and at sea over the dispute, but have avoided actual conflict.

Japan has said its military scrambled a record number of jets last year, mostly in response to an increase in approaching Chinese aircraft. Tokyo ordered its jets to the skies 1,168 times in the fiscal year until March, with 73 per cent of the missions against aircraft either known to be or believed to originate from China.

In the US case, the Americans are questioning the manoeuvres of the Chinese pilots and the speed at which they flew. While Lieutenant-Colonel Lori Hodge, spokesman for the Pacific Air Forces, did not give further information on the exact manoeuvres carried out by the Chinese jets, CNN reported earlier that the jets came within 46m of a US Air Force plane flying over the Yellow Sea. One of the fighters even flew upside down directly over the American plane, said CNN.

The US Air Force is discussing the event via the Military Maritime Consultative Agreement meeting and diplomatic channels.

The intercepted American aircraft was a WC-135, designed to collect information on radiation in the atmosphere to detect nuclear explosions. China and the US have been in talks about ways to curb the nuclear weapons development programme in North Korea, which is in the vicinity.

In February, the US Pacific Command reported an unsafe encounter between surveillance planes from the two sides near the disputed Scarborough Shoal.

Chinese state media said that Chinese pilots took legitimate and professional measures.

AGENCE FRANCE-PRESSE, BLOOMBERG