WARSAW, March 4 (Reuters) - Poland has signed a deal to buy anti-tank grenade launchers from Sweden's Saab in a deal worth around 6.5 billion zlotys ($1.63 billion), its Defence Minister Wladyslaw Kosiniak-Kamysz said on Monday.

This year Poland is spending about 4% of gross domestic product (GDP) on defence as it seeks to strengthen its armed forces in the face of Russia's invasion of Ukraine.

"Poland's armed forces will... (get) anti-tank grenade launchers produced in Sweden, and we are allocating about 6.5 billion zlotys for that," Kosiniak-Kamysz told a news conference, adding that the weapon had been effective in Ukraine.

The deal concerns the Carl-Gustaf M4 grenade launcher, which is intended to combat all types of modern combat vehicles.

Kosiniak-Kamysz said Poland would receive several thousand grenade launchers and several hundred thousand rounds of ammunition, as well as the necessary infrastructure, training and other elements necessary to use the weapon.

($1 = 3.9810 zlotys) (Reporting by Alan Charlish and Karol Badohal; Editing by Jan Harvey)