HONG KONG -- China on Friday denied Japanese accusations that its ships directed a radar capable of aiding weapon strikes at a Japanese naval vessel and helicopter near disputed islands recently, then lobbed its own accusation: that Japan was trying to fan tensions. The latest exchange underscored the depth of a festering discord between the two countries, and trading partners, over the territorial dispute.
The tit-for-tat accusations started on Tuesday, when Japan's Ministry of Defense announced that a Chinese military vessel had trained a radar on a Japanese naval destroyer near the islands in the East China Sea on Jan. 30. The ministry said a Chinese frigate had directed the same kind of radar at one of its military helicopters on Jan. 19.
Because using such "fire control" radar can precede an attack, the Japanese defense minister, Itsunori Onodera, said that a misstep "could have pushed things into a dangerous situation."
China did not respond at the time, but on Friday the Defense Ministry Web site said that the naval vessels' radar had "maintained normal observational alertness, and there was no use of fire-control radar." It did not explain what it meant by "normal observational alertness," though the ministry added that the Japanese claims were "out of step with the facts."
For all China's vehemence, the statement by its Defense Ministry suggested that senior officials in Beijing wanted to avoid an escalating quarrel, said Denny Roy, a senior fellow at the East-West Center in Honolulu who researches security issues.
"I think it's a positive development that the Chinese would deny doing this, as opposed to saying, 'Yes we did it, and we'll do it again,' " Mr. Roy said. "For the Chinese to not want to be portrayed as an aggressor, I think, is a good sign."
By contrast, when Japan complained in early January that Chinese ships had entered Japanese-controlled waters near the islands for 13 hours the ambassador responded that the islands belong to China and the Japanese ships that had no right to be there, according to Japanese officials. That incursion was particularly long, but it came amid weeks of cat-and-mouse games between ships and occasionally planes from both countries.
This time, the Chinese Defense Ministry accompanied its denial with accusations that Japan was to blame for any unnervingly close encounters between their ships and aircraft near the islands known as the Diaoyu in China and the Senkaku in Japan, which has controlled them for decades.
Japan was "deliberately creating a tense atmosphere and misleading international opinion," the Defense Ministry said.
Later on Friday, the Chinese Foreign Ministry also dismissed Japan's assertions as "spun out of thin air."
"We have no choice but to stay highly vigilant about Japan's true intentions," Hua Chunying, a Chinese Foreign Ministry spokeswoman, told reporters.
Long-standing tensions over the islands flared in September, when the Japanese government bought three of the five islands from a private owner in what it said was an effort to keep them out of the hands of a Japanese nationalist. China, however, said the purchase amounted to a provocative denial of its territorial claims, and sometimes violent protests broke out in dozens of Chinese cities.
In the months since, the Chinese government has underscored its claim to the islands by sending government vessels and military ships and aircraft to the waters near the islands which are patrolled by Japanese Coast Guard ships.
In Tokyo, Japan's Chief Cabinet Secretary Yoshihide Suga responded Friday to China's denial about the radar, saying, "We cannot accept China's explanation."
"We urge China to take sincere measures to prevent dangerous actions which could cause a contingency situation," he said.
Japan earlier said that Russian fighter planes had briefly entered its airspace on Thursday, raising tensions in a separate dispute between those two countries over another set of islands. Russia denied any incursion.
Bree Feng and Patrick Zuo contributed research from Beijing.
This article originally appeared in The New York Times.