French police have detained 150 people in an operation against undocumented migrants in the port of Calais, officials say. More than 300 officers were involved in the operation on Tuesday morning, regional state authorities said.

The port has become a magnet for migrants trying to enter the UK illegally across the English Channel.

There are estimated to be about 1,000 migrants living in makeshift camps around Calais.

The police operation came two days before Immigration Minister Eric Besson was due to visit Calais for talks on the migrant situation, according to a state spokeswoman, quoted by AFP news agency.

"It is an attempt to dismantle people-trafficking networks," she said.

"It is an operation to destabilise the networks and try to find the smugglers."

She added that a security cordon had been thrown up around a migrant camp.

Many of the 150 people arrested said they were from Afghanistan, the spokeswoman said. They have been taken into custody in Calais, Boulogne and Lille.

Centre closed

A refugee centre at Sangatte, near Calais, was closed in 2002 and bulldozed, under pressure from Britain.

Migrants who have since set up squatter camps around the port receive no help from French authorities, but charities have stepped in with donations of food and clothing.

A BBC correspondent, who recently visited the camps, said migrants had complained that the hard-line French riot police, the CRS, had been making life difficult for them.