WARSAW, Poland — Poland’s President Andrzej Duda signed a law Monday that will eventually increase the country’s spending on defense to at least 2.5 percent of GDP, well above the 2 percent required by membership in NATO.

It is part of an effort by Poland’s conservative government to improve the nation’s defenses in reaction to security concerns created by Russia’s intensified military activity in the region.

Poland is one of just five NATO members, an alliance of 28, that already spends 2 percent of GDP on defense. Under the new law it will raise spending to 2.1 percent in 2020 and to at least 2.5 percent in 2030.

“No one needs explaining that we want to have a strong, efficient armed forces,” Duda said in announcing his decision. “A force that will at a time of threat to Poland will be capable of defending Poland’s borders, of defending the security of its citizens.”

Duda noted that the bill was backed by both the ruling conservative party and the opposition, something rare in Poland’s divided political atmosphere.

The bill will also increase the number of troops serving in the military from the current 100,000 to 200,000. Some 50,000 of them will belong to new voluntary structure, the so-called Territorial Defense Force.