Tokyo, April 17:

Japan today voiced concern and pressed for answers after China drove away Japanese ships from contested gas-rich waters in the latest dispute between the neighbours.

China has declared that only its own ships involved in energy development can enter the area straddling the two countries’ exclusive economic zones in the East China Sea. At least two Japanese fishing boats have been turned away, according to Tokyo.

“We have expressed our concerns to China that it may be violating Japan’s sovereign rights and may be breaching international laws of the sea,” chief cabinet secretary Shinzo Abe said, “We have requested that they reply to us on the details of the matter quickly and clearly.” Prime Minister Junichiro Koizumi called for calm.

“I wonder what they want to do,” Koizumi said of China, “I would like to deal with this cool-headedly.” The two nations, among the world’s top energy importers, have been sparring for years over potentially lucrative gas fields in a part of the East China Sea where their 370-km exclusive economic zones overlap.

China began drilling unilaterally in the area in 2003. Japan accuses China of crossing into its sector and last year gave the go-ahead for Japanese firms to start exploration. China’s Maritime Safety Administration declared the no-sail zone from March 1 to September 30, saying that Chinese ships will be laying cables and pipelines and conducting other work day and night.

Outside vessels are not allowed to enter the area and must keep a distance of at least one nautical mile from ships involved in the project, the maritime authority said on March 1. Chinese authorities turned away Japanese fishery boats on March 3 and March 24.