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.”