Thirty-five migrants have been found in two Sofia-plated vehicles in northwestern Bulgaria, police say.

Two Bulgarian nationals have also been detained for 72 hours on suspicions of people smuggling activities.

The vehicles, a car and a van, were stopped for a routine check near the village of Staropatitsa, not far from the border with Serbia, Focus News Agency quotes the regional police department in Vidin.

The foreign nationals, who, evidence suggests, "unlawfully crossed the territory of the country," were from Pakistan, Afghanistan, and Iraq.

The latest operation comes amid accusations from Belgrade that Bulgaria allows Middle Eastern migrants to cross into Serbia via its territory.

Last week the Serbian government allowed the formation of joint police and army units that would patrol along the country's borders with Macedonia and Bulgaria to deal with lax controls.