BELGRADE (Reuters) - The Serbian authorities on Wednesday imposed restrictions on the movements of migrants in a camp near Belgrade, after three men allegedly attacked a woman and her children near the refugee center, a minister said.

The migrants will now need permission to leave the camp, a set of former army barracks in the town of Obrenovac, just outside Belgrade, said Labour Minister Aleksandar Vulin, who is also in charge of refugee centres.

"We are introducing tougher measures ... they will have to return to the camp by a certain time and they will be issued identification documents," Vulin said, according to the Tanjug news agency.

Although the so-called Balkan route to Western Europe was shut last year, migrants continue to flow through Serbia to its northern border with Hungary. Over 7,000 migrants, mainly from Afghanistan, remain in the country, which is culturally and financially ill-equipped to care for them.

About 500 of the migrants live in Obrenovac. They were moved there over the past 10 days from makeshift shelters in warehouses in Belgrade as temperatures dropped below freezing.

The lockdown was imposed after a local woman complained that three men she described as migrants attacked her while she was walking with her three children near the Obrenovac camp. Police said they were investigating the incident.

Vulin also said the authorities had introduced a special bus to take migrants back and forth between Obrenovac and Belgrade, "to avoid mixing" with local population.

(Reporting by Aleksandar Vasovic; Editing by Larry King)