KYIV, Ukraine (AP) — Ukrainian President Volodymyr Zelenskyy said Thursday his country has developed a weapon that hit a target 700 kilometres (400 miles) away, in an apparent reference to the previous day’s strike on an airport in western Russia.

Zelenskyy said on his Telegram channel the weapon was produced by Ukraine’s Ministry of Strategic Industries but gave no other details.

On Wednesday, a four-hour wave of drones that Moscow blamed on Ukraine hit an airport near Russia’s border with Estonia and Latvia, damaging four Il-76 military transport planes, according to local reports.

The airport is in Russia’s Pskov region, about 700 kilometres (400 miles) north of the Ukrainian border.

In all, six Russian regions were targeted in the barrage amid the 18-month war.

The Associated Press was unable to determine whether the drones were launched from Ukraine or inside Russia.

Kyiv officials normally neither claim nor deny responsibility for attacks on Russian soil, though they sometimes refer obliquely to them. Zelenskyy’s remark was the clearest hint that Ukraine was behind the strike.

The attack forced the closure of Pskov airport, though it reopened Thursday, according to Russian transport officials.

Another drone intercepted overnight near Moscow resulted in flight delays at several airports around the Russian capital, officials said Thursday. No injuries were reported.

Russian news agency Interfax reported, meanwhile, that security services killed two people and detained five members of a Ukrainian sabotage group in the Bryansk border region on Wednesday.

The apparent Ukrainian drones reaching deep into Russia and cross-border sabotage missions are part of Kyiv’s efforts to heap domestic pressure on the Kremlin, militarily and politically. Meantime, a Ukrainian counteroffensive launched in June is chipping away at some parts of the front line, Kyiv officials claim.

Ukraine is aiming to “erode Russian morale and increase pressure on its commanders,” the International Institute for Strategic Studies, a think tank, said in an assessment.

The strategy is “to bring Russian forces to a tipping point where combat power and morale may begin to break,” the IISS said in the analysis late Wednesday.