Hungarian police discovered a tunnel under the wire fence on the border with Serbia at the weekend and prevented more than 300 migrants from illegally crossing the border, the Serbian public broadcaster RTS said on Monday.

A 24-metre-long tunnel was discovered in cooperation with the military near the spa town of Morahalom. It was believed to be used by migrants to illegally cross the border and carry on their journey to western Europe.

It was the third underground passage under the wire fence discovered in this region in the past year, RTS said.

Hungarian border police arrested 54 people while attempting to jump over or cut through the border fence while 258 migrants were found in the border area without documents. Most of them identified themselves as Syrians, but there were also Iraqis, Iranians, Afghans and Palestinians.

Since the end of May, Hungary has seen a large increase in the number of migrants trying to enter the country illegally, with nearly 900 such attempts reported last week alone.

Hungarian officials have repeatedly said that Hungary will not remove the wire fencing from the border, but will increase the defence of the Schengen area to prevent migrants from entering the European Union illegally, RTS said.

Attempts to cross the border illegally have also been reported in areas near the Serbian border with Croatia. Special police forces were deployed in the Sid area last month to protect the local population from migrants, RTS said.