Poland introduced temporary controls on its borders with Germany and Lithuania on Monday in an effort to stem what the government says is an increasing number of undocumented migrants crossing from the north and west.

Polish authorities said on Monday that new checks at the German border had already stopped several people from entering the country illegally, as German lawmakers warned of the consequences of Poland's stricter controls.

SLUBICE, Poland — Poland reinstated border controls on Monday with neighboring Germany and Lithuania following similar German restrictions imposed earlier this year aimed at discouraging asylum-seekers.