Groups representing immigrants in Spain have called for greater protection from the authorities, after three nights of violence.

Nearly 40 people were injured in anti-immigrant attacks in El Ejido, near the south-eastern port of Almeria.

Left-wing opposition politicians and immigrant rights groups angrily criticised police for failing to take tougher action to prevent the attacks.

Some 150 Moroccan agricultural workers held a peaceful protest outside the town's main police station on Tuesday, refusing to return home until authorities guaranteed their safety.

"If any of us leave this spot, they will kill us," Fuad Zarrik said.

State radio said some immigrants were so frightened they were packing up and leaving town.

El Ejido is the centre for fruit and vegetable production - an industry that relies heavily on cheap immigrant labour.

'Violate friendship'

The violence against North African immigrants erupted on Saturday when a Moroccan man was arrested on suspicion of stabbing to death a Spanish woman in a local market.

The death came two weeks after another Moroccan man was arrested in connection with the stabbing to death of two people.

In response to the murders, hundreds of Spaniards marched through the town shouting racist slogans.

Police reinforcements were called in after protesters went on the rampage, burning cars and shops belonging to Moroccans.

A pall of acrid smoke hung over the town after rioters burned down a nearby plastics factory on Monday night.

Morocco issued a protest on Tuesday.

"The Moroccan government strongly deplores racist acts against Moroccans which are a violation of friendship and good neighbourliness between the two countries," the foreign ministry said.

Spanish Foreign Minister Abel Matutes appealed for calm, saying that Spaniards must get used to the influx of North African immigrants attracted by the fast-growing economy.

He told state radio: "We need to reflect on how we need to change our behaviour in a pluralist society that with each day will ... have more immigrants, that each day will need more immigrants to take our country forward."