The bodies of 13 illegal immigrants have been found on the shoreline near the Spanish city of Tarifa.

The group - eight from sub-Saharan Africa and five from north Africa - are believed to have drowned while trying to swim to shore.

We do not rule out finding more bodies

Police spokeswoman

A police helicopter on an early morning patrol of the narrow strait between Spain and Morocco had previously spotted people in a boat.

Southern Spain is known as a popular entry point into Europe for thousands of illegal immigrants.

Last year Spain expelled or refused entry to nearly 45,000 immigrants, according to official statistics.

Human trafficking

A Spanish guard patrol came upon the bodies early on Thursday morning along a deserted stretch of coast near the town of Barranco Hondo.

Two or three of dead were pregnant women, according to the police.

Spain's Interior Minister, Angel Acebes, said the dead migrants were victims of human trafficking.

"The people responsible for these deaths are only and exclusively the organised mafia networks that use human lives for their own benefit," he said.

Army divers based in Ceuta, one of Spain's two enclaves on the Moroccan coast, are searching the waters for more victims.

"We do not rule out finding more bodies," a police spokeswoman said.

Shortly after the bodies were found, police arrested eight Africans further along the Tarifa coast. They may have been on the same boat as the 13 victims.

Dangerous gamble

The rocky shore at Tarifa is a popular entry point for thousands of illegal immigrants.

Located on Spain's southern-most tip, the city is separated from Morocco by only the 14-kilometre ( 8.75-mile) wide Strait of Gibraltar.

According to the Moroccan Workers and Immigrants Association in Spain, some 4,000 people have died or disappeared since 1997 in the Strait of Gibraltar and the Atlantic waters between Africa and Spain's Canary Islands.

A police helicopter spotted people in a boat earlier in the day

In February, 10 people died while trying to cross from Morocco into southern Spain.

And on 24 July, another 14 people were declared missing, including a child whose parents later made it across the strait to Tarifa.

The two Moroccans who smuggled that group into Spain were imprisoned and charged with involuntary homicide.

The issue of illegal immigration has become a bone of contention between Spain and Morocco.

The uneasy ties between the two countries erupted into crisis in July when Moroccan troops occupied the tiny disputed island of Perejil, which is claimed by Spain.

Spain responded by sending its military to take the island by force.