MADRID, Sept 20, 2008 (AFP) - A plane returning over 100 illegal migrants to Gambia was forced to go back to Spain after the authorities refused to allow them to disembark, a police official said Saturday.

The plane carrying 101 Gambians expelled from Spain and 117 Spanish police officers was stranded on the tarmac at Banjul airport for seven hours on Friday, the official, who asked not to be named, said.

Spain's interior and foreign ministries declined to comment on the reason for the decision, but the official said it had been financial.

The Spanish police were carrying 300 euros (430 dollars) per migrant but the Gambian authorities wanted more, the official said.

Gambian authorities also delayed the plane's return to Spain by not clearing it for take-off for around five hours, the official added.

The plane eventually returned late Friday to Las Palmas in the Spanish Canary Islands.

In October 2006, Spain and Gambia signed an agreement on the repatriation of Gambian nationals arrested in Spain for being illegal migrants.

According to Spanish media, the Foreign Affairs ministry had restarted negotiations with the Gambian authorities about the repatriation.

In August, Mauritania also refused to allow a group of illegal migrants returning there to disembark, forcing the plane to return to Spain.

Meanwhile, a boat carrying 100 Africans arrived Saturday in Tenerife, one of the Canary Islands. The boat arrived following a six-day journey from Mauritania, officials said.