South Korea took unspecified “tactical action” to deter Russian jets after they crossed its air buffer zone unannounced Tuesday, in a move that could suggest Seoul responded by sending its own planes to the sky.

South Korea’s Joint Chiefs of Staff was reportedly short on details but is statement said the move was made in order to prevent accidental clashes along its air defense identification zone.

Russian media reportedly claimed that South Korea responded to the two Russian Tu-95 bombers and one Sukhoi Su-30 fighter jet that flew over the waters separating Japan and the Korean Peninsula by sending its own F-16’s into the air, though South Korea has not validated these claims.

A Russian state-owned news outlet claimed that Moscow officials said the air defense identification zone was unilaterally established by South Korea and therefore is not binding for other states.

It remains unclear what Russian aircraft were doing flying in between Japan’s and South Korea’s airspace, but the news comes one day after Washington and Seoul launched some of their largest joint military drills in years.

The military exercises are said to be in response to North Korea’s aggressive nuclear posture and will include field exercises involving aircraft, warships, tanks and potentially tens of thousands of troops.

The drills, which are set to last through Sept. 1, are expected to be taken negatively by Seoul’s northern neighbor, but are intended to shore up U.S.-South Korean defenses.  The renewed defensive posture also comes as the U.S. is beefing up its alliances in Asia as China and North Korea have signaled they are strengthening ties with Moscow amid Russia’s war in Ukraine.