SOFIA - Bulgaria detained 45 migrants who were trying to cross into neighbouring Serbia, the interior ministry said on Tuesday, three days after Belgrade bolstered its border patrols to prevent migrants getting in.

More than 160 people others were detained in the capital Sofia, the interior ministry said, as the country tries to stop its territory being used as a transit route to western Europe by people fleeing war and poverty in the Middle East.

Serbian Prime Minister Aleksandar Vucic said on Saturday his country must not become a “collective centre for migrants” most of whom enter Serbia from Bulgaria seeking to travel on to richer European countries.

Thirty of the 45 migrants detained at the border were Afghans, 13 were from Pakistan, and two from Iran, authorities said.

The Bulgarian Interior Ministry’s Chief Secretary Georgi Kostov said on Monday that Serbia should not be concerned about security at the border, saying migratory pressure was “normal considering the season”.

Migrant flows into Bulgaria have eased slightly. The country detained about 14,000 migrants in the first six months, compared with 21,000 in the same period last year.

Very few migrants want to stay in the European Union’s poorest state, preferring to journey onwards to wealthier EU countries like Germany and Sweden.

Bulgaria has bolstered its border patrols with Turkey following an attempted coup there, but said there were no signs of an increase in refugee flows.