Hundreds of members of pro-defense forces have marched in downtown Warsaw to show their readiness to defend Poland if needed, amid concerns over the conflict in neighboring Ukraine and Russia's role in it.

The Federation of Pro-Defense Organizations was formally initiated in cooperation with the armed forces in March, in response to grassroots actions by ordinary Poles and paramilitary organizations. It includes scouts and students who want to join the police and military, or support them.

Their first nationwide rally Thursday marked the anniversary of the 1939 Soviet invasion of Poland, which was fighting Nazi Germany at the time. The timing highlighted the concerns over unrest across Poland's and the European Union's eastern border.

Hundreds of uniformed young people marched in front of the Tomb of the Unknown Soldier.