"The exercise takes place in the air, on the ground and at sea in large parts of the country," the Swedish Armed Forces said, announcing the exercise which is scheduled to run until May 11.

The focus will be on southern and northern Sweden and the strategically important island of Gotland.

The United States, the United Kingdom, Finland, Poland, Norway, Estonia, Latvia, Lithuania, Ukraine, Denmark, Austria, Germany and France are all also taking part.

With most of the participants NATO members, the exercises are spotlighting Sweden's ongoing struggle to join the military alliance.

Ending two centuries of neutrality and military non-alignment Sweden, along with neighbouring Finland, announced bids to join NATO in May 2022, in the wake of Russia's invasion of Ukraine.

But while Finland managed to become the 31st member of NATO on April 4, Sweden's bid still faces opposition.

New members need to be unanimously ratified by all members of the alliance, and Sweden still faces opposition from Ankara and Budapest.

Sweden has especially angered Turkey by refusing to extradite dozens of suspects that President Recep Tayyip Erdogan links to a failed 2016 coup attempt and a decades-long Kurdish independence struggle.

NATO diplomats hope Erdogan will become more agree to ratification if he wins elections next month.

The Nordic nation has had close ties with NATO ever since joining the Partnership for Peace programme in the 1990s, but as a non-member, it is not covered by the security guarantees of NATO's Article 5 on collective defence.

While surrounded by alliance members, as the only Nordic country outside NATO, experts say Sweden could become a strategic interest for Russia in the event of a conflict.