Morocco on Wednesday vowed further crackdowns on illegal migrants after rounding up hundreds of foreigners close to the Spanish enclave of Melilla, in a move criticized by local rights groups.

The interior ministry said the operation Tuesday evacuated a forest "where migrants live in very precarious conditions."

Over 600 African migrants charged the border fence separating the Spanish enclave of Melilla from Morocco on Tuesday, with at least 35 managing to climb the dangerously high barrier, including five who were injured, Spain's government said.

They were the latest in a flow of thousands of migrants trying to reach Melilla and the other Spanish north African territory of Ceuta, which together make up Europe's only borders with Africa.

Police on Monday arrested three African migrants accused of attacking officers who intercepted a boat with 17 people on board, including children and pregnant women, trying to reach Spanish soil.

Civil Guard boats stopped the vessel off Melilla, a Spanish enclave in northern Morocco, Spanish government officials said in a statement.

Some 350 African migrants tried to storm a fence from Morocco into Spanish territory on Wednesday, authorities said, the latest in a wave of desperate arrivals at Europe's southern border.

Just three of the migrants who charged towards the seven-meter (23-foot) fence in separate locations at dawn made it into the territory of Melilla, the Spanish government delegation there said in a statement.

The U.N. on Tuesday warned Spain over plans to instantly deport migrants who clamber over the border fence into its north African territories, saying Madrid could end up breaking international law.

"UNHCR is concerned over a proposal by Spain to legalize automatic returns of people trying to cross border fences into its enclaves of Ceuta and Melilla," said the U.N. refugee agency's spokesman William Spindler.

About 60 Africans scrambled over a border fence from Morocco into Spanish territory Monday, as a U.N. official urged Spain to protect migrants' rights following evidence of police abuse.

It was the latest in a string of attempts by desperate Africans trying to reach European soil by scaling the seven-meter (23-foot), triple-layer fence into the Spanish territory of Melilla, raising pressure on Spain's government.

Hundreds of African migrants tried Thursday to leap a triple-layer border fence around Spain's north African territory of Melilla but only one person made it through, the Spanish government said.

About 250 people attempted to cross the six-meter (20-foot) high fence between Morocco and the Spanish city of Melilla in the early morning, the Spanish government representative in Melilla said in a statement.

Spain rescued Tuesday nearly 500 African migrants trying to enter the country by boat while hundreds more tried to scramble over a border fence into the Spanish territory of Melilla.

Spain's coastguard said it picked up 470 sub-Saharan Africans who were crossing the Strait of Gibraltar in 49 small boats, part of a surge of migrants across the Mediterranean to Europe's southern shores.

More than 400 migrants stormed across a towering, triple-layer border fence from Morocco into the tiny Spanish territory of Melilla on Wednesday, one of the biggest crossings in nearly a decade, officials said.

About 1,000 sub-Saharans joined in the dawn attempt to enter Melilla, a tempting target for Africans desperate to reach Europe as it forms one of the only land crossings along with another Spanish territory, Ceuta, to the west.

More than a hundred people stormed the fence between Morocco and the Spanish enclave of Melilla on Thursday, officials said, in the latest attempt by migrants to breach the border.

The early-morning surge of 500 people "ended with 140 immigrants of sub-Saharan origin entering national territory," according to a statement from Spanish officials in the city.