MADRID (Reuters) - More than 600 African migrants forced their way through the heavily fortified border fence separating the Spanish North African enclave of Ceuta from Morocco on Thursday, using circular saws, shears and mallets to cut through the wire.

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Around 800 migrants tried to push through the barrier at dawn, the Interior Ministry said in a statement, deterring police from intervening by hurling plastic bottles of excrement, quick lime and using makeshift flame throwers.

Migration has become a political issue in Spain since Socialist Prime Minister Pedro Sanchez took office in June and shortly thereafter agreed to receive more than 600 migrants aboard a charity-run ship rejected by Italy and Malta.

Illegal migration to Spain has been increasing steadily for more than a year and arrivals by sea have risen dramatically in recent weeks with the arrival of warmer weather, straining services in some towns in southern Spain.

While the numbers of migrants crossing the land border in Ceuta has remained stable, irregular arrivals by sea have more than doubled from last year to almost 17,000 so far this year, according to Interior Ministry figures.

The recent spike in migrant arrivals is making it hard to process and accommodate the incomers, authorities and charities said on Thursday. Coast guard unions have called on the government for more resources to help with the influx.

The government held a crisis meeting with rescue services, police and charities on Wednesday to find emergency accommodation for 400 recently arrived migrants in the southern region of Andalusia.

Over 200 rescued migrants were forced to sleep on the rescue boats that brought them to shore this week in the town of Algeciras because there was nowhere to accommodate them, a city council spokesman said on Thursday.

“The processing center we have is overwhelmed,” he said.

Algeciras overlooks the narrow Strait of Gibraltar which separates Africa from Europe at just 14 kilometers (nine miles) at its narrowest point and has become a key route for migrants seeking to enter Europe.