"We cannot control the land and sea borders, which are very wide - we can't withstand this growing pressure. We need help," said Sidi Mohamed Ould Boubacar, the Mauritanian prime minister, in an interview published in Spain's El Pais newspaper.
Traffic on the established migration route between Mauritania and Spain's Canary Islands has grown in recent weeks, with scores of young Africans leaving the Mauritanian coast every night in rickety fishing boats, hoping to find work in Spain.
Spanish ministers have pledged their support to the west African country and the secretaries of state for foreign affairs and security, Bernardino Leon and Antonio Camacho, flew in to meet their Mauritanian counterparts on Thursday.
"We are going to put in place control systems developed jointly between the European Union, Spain and Mauritania," Leon said.
Succeed or Die
Many have died making the dangerous 800km (500 miles) journey and the Red Cross estimates that more than 1000 African migrants had died since the start of this year trying to get to Europe by ever longer sea routes.
A Spanish hospital ship recovered the bodies of 24 migrants around 140km (85 miles) off the Mauritanian coast on Wednesday while at least 34 were detained overnight in already crowded police stations after their attempts to cross failed.
Around 170 migrants are being detained in police stations around the Mauritanian town of Nouadhibou, and 70 more detained at sea are on their way, officials from the Red Crescent aid agency said.
Local officials estimate there are 10,000-15,000 West Africans, mostly from Senegal and Mali, in and around Nouadhibou trying to scrape together enough money to make the crossing.
A network of fixers can book a place in long, thin traditional fishing boats called pirogues for 150,000 ouguiya ($550), much cheaper than the old route through Spain's North African enclaves of Ceuta or Melilla, migrants say.
"Die or succeed is the motto," said Mamadou Ba, from Senegal, who like his fellow would-be migrants was eager to be repatriated and freed quickly so he could make the journey once again.
"Each hour that I lose here, I'm losing a lot of my future," he said, lying under a blanket on the police station floor.