Nato has been forced to scramble jets in response to Russian violations of Lithuania's airspace.

Two Russian military aircraft, an Su-30 fighter jet and an II-78 refuelling tanker, entered the Nato member state on Thursday for approximately 18 seconds, prompting a formal reaction from the Alliance. They were possibly on a refuelling training mission when they flew 700m (0.43 miles) at 1500 GMT, the military said.

"I strongly condemn the violation of Lithuanian airspace by the fighter jet and transport plane of the Russian Federation from a Kaliningrad region site," Lithuanian president Gitanas Nausėda said in a statement.

"This is a blatant breach of international law and territorial integrity of Lithuania," he added on X. "Once again, it confirms the importance of strengthening European air defence readiness."

Russia's defence ministry has denied the incident and said none of its Su-30 jets training in the Kaliningrad region violated the territory of any country. The Russian province is sandwiched between Poland and Lithuania.

Nato's Baltic Air Police scrambled Spanish Eurofighter Typhoon jets that were patrolling the area in response. It deployed aircraft to the Lithuanian airbase of Siauliai as part of its Operation Eastern Sentry.

A Nato official told Reuters that the swift response demonstrated "Nato's readiness to respond to any developments and ability to ensure the safety of the Alliance's airspace".

Lithuania summoned Russia's top diplomat to issue a stern protest after the incident. It has informed the Alliance, European Union allies and the North Atlantic Council of the episode, the country's foreign ministry said.

"This incident once again shows that Russia is behaving like a terrorist state, disregarding international law and the security of neighbouring countries," Lithuanian Prime Minister Inga Ruginiene said on Facebook.

"Lithuania is safe. Together with our allies, we look after and will defend every centimetre of our country."

The latest incursion follows a spate of similar events starting with more than 20 Russian drones entering Poland last month, prompting its foreign minister Radoslaw Sikorski to request that a no-fly zone be implemented.

Former Deputy Supreme Allied Commander of Nato, Sir Richard Shirreff, told The Independent that he believes the incursion was a "deliberate attack to probe Nato defenses", adding that if Russia "smells weakness" it will persist in its aggression: "Nato has to respond with real strength."

Nine days later, Russia's military jets were accused of violating Estonia's airspace for 12 minutes on 19 September. Russia denied its planes entered the country and accused the Estonia of purposefully inflaming tensions between Russia and Europe.

Violations were also alleged to have taken place in Romania, as training drills got underway in Belarus. Denmark later accused Russia of encroaching its airspace, which Russia has denied.

Nato scrambles fighter jets after Russian incursion into Lithuania's airspace