China Coast Guard vessel No. 31239 sails in the East China Sea near the disputed isles known as Senkaku isles in Japan and Diaoyu islands in China, in this handout photo taken and released by the 11th Regional Coast Guard Headquarters-Japan Coast Guard December 22, 2015. REUTERS/11th Regional Coast Guard Headquarters-Japan Coast Guard/Handout via Reuters

TOKYO (Reuters) - A Chinese coastguard vessel with what appeared to be gun turrets entered territorial waters claimed by Japan in the East China Sea, Japan’s coastguard said on Saturday, adding that it was the first such incursion by an armed Chinese vessel in the disputed area.

The vessel was one of three that appeared in the waters off the disputed Senkaku Islands, known in China as the Diaoyus, shortly after 9:30 a.m. (0030 GMT) and left Japanese-claimed waters about 70 minutes later, a Japan coastguard spokeswoman said.

The vessel had first been sighted in the area on Tuesday afternoon and was sailing 29 km (18 miles) off one of the contested islands as of 9:00 a.m. (0000 GMT) on Wednesday, according to Japan’s coastguard.

At that time, China said its vessels were carrying standard equipment and doing nothing wrong in Chinese waters.

Chinese coastguard vessels sail regularly near the islets but the Japanese coastguard spokeswoman said none had ever been seen equipped with arms.

The dispute over the Japan-controlled islands has been a major sticking point in the two countries’ often contentious relations in recent years.