Japan rejects North Korea's accusation that the sinking of an unidentified ship after a shootout with Japanese patrol boats was "an act of piracy," Chief Cabinet Secretary Yasuo Fukuda said Thursday.

"I believe the expressions used were 'brutal piracy' and 'terrorism of a modern brand.' I wonder if these are phrases that are suitable internationally," the government's top spokesman told a news conference.

"We are taking appropriate actions based on international laws and other related laws. Such criticism expressed in a poor and vulgar manner is totally inappropriate," Fukuda said.

The suspected spy ship, pursued by the Japan Coast Guard after entering Japan's 200-nautical-mile economic zone, sank in the East China Sea on Saturday night after an exchange of fire with Japanese patrol boats. About 15 people on the boat were lost at sea.

Meanwhile on Thursday, Pyongyang described Japan's conduct as "a grave and sacrilegious act that will never be forgiven."

"What cannot be overlooked is the fact that Japanese authorities are spreading a rumor linking the incident to us with no evidence at all," said the (North) Korean Central News Agency (KCNA), quoting a spokesman for the North Korean Foreign Ministry.

The spokesman warned that North Korea will probably adopt countermeasures, depending on Japan's future response, but declined to elaborate.

"Japan's overt act of war in waters outside its territory speaks of its extreme ambition of rearmament and foreign expansion," he said.

The remarks came a day after Pyongyang denied that the unidentified ship in question is North Korean and called Tokyo's claims in this regard as a "trite charge and provocation."

Praise given online

Virtually all the e-mail messages that the Japan Coast Guard has received since last Saturday's shootout, in which a suspected North Korean spy was sunk, has been supportive of the coast guard's response.

Coast guard officials said the agency has received 577 messages from the public after the gunbattle, with 98 percent lauding its action.

Only 14 messages were critical of the coast guard's conduct.