EU countries have been fearing a possible influx of people from Afghanistan after the Taliban seized control on August 15, with memories still fresh from the migrant crisis that shook Europe in 2015.

"The pressure on Bulgaria's borders is increasing," Defence Minister Georgi Panayotov said in a statement.

The soldiers being deployed "will carry out a protection mission," he said, adding that they would be available to help police and gendarmes with "constructing barriers and surveillance".

The interior ministry has said an increased number of undocumented Afghan migrants have been detained in the past week.

Bulgaria is on one of the main routes used by people attempting to reach Europe from the Middle East and Afghanistan.

Between 2013 and 2018 it erected a barbed-wire fence along its 260-kilometre (160-mile) border with Turkey, but a lack of maintenance meant that the border did not remain totally sealed.

Bulgaria, the EU's poorest member state, has not itself taken in a large number of refugees.

Most of them have travelled further west after arriving in the country.

The EU's perennial divisions on the question of migration and refugees may be on show again on Tuesday at a meeting of the bloc's interior ministers, where the fall-out from the Taliban takeover of Afghanistan will be on the agenda.