Moroccan security forces intervened Tuesday after a record 6,000 migrants crossed largely unimpeded into a Spanish North African enclave amid diplomatic tensions between Rabat and Madrid.

Reinforcements deployed at Morocco’s Fnideq border crossing with the enclave of Ceuta and fired tear gas to disperse a large crowd of would-be migrants who had gathered in the hope of seizing a rare opportunity to slip across, an AFP correspondent reported.

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The surge in numbers came after some migrants were able to cross into the tiny Spanish territory of some 84,000 people virtually unimpeded by Moroccan border guards.

The Moroccan government has been angered by Spain’s decision provide medical treatment for the leader of the Western Sahara independence movement who has been seriously ill with Covid-19.

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Spanish Prime Minister Pedro Sanchez called off a planned trip to Paris to oversee his government’s response while the EU commissioner for home affairs, Ylva Johansson, urged Morocco to take action to stop the “worrying” increase in the number of migrants crossing illegally.

Spain sent back around a quarter of the 6,000 or so migrants, mostly Moroccans, who entered the Ceuta enclave in the past 36 hours and was preparing further repatriations, Interior Minister Fernando Grande-Marlaska told public television.

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Monday’s arrival figures were the highest ever for a single day, authorities in Ceuta said.

Early Tuesday, another 300 migrants, said to be from sub-Saharan Africa, attempted to cross into Spain’s other North African enclave of Melilla by scaling a high barrier.

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Authorities in Melilla said “85 men and one woman succeeded in entering”.

Amal, 18, said he had hurried to the Ceuta border with his brother and two friends in the hope of slipping into Spanish territory.

“Many of our friends managed to get across. We came later when we heard about it,” he said.

“We tried to climb over the mountain but the police blocked us”.

The migrants reached Ceuta by swimming or by walking at low tide from Moroccan beaches a few kilometres to the south. Some used inflatable swimming rings and rubber dinghies.

In the early hours of Tuesday, hundreds more men and women of all ages flocked to the border to try their luck.

They walked down a path to the beach in their dozens, before running towards Ceuta along the coastline, as a handful of Moroccan policemen watched on without intervening.

“I saw on Facebook that it was possible to cross the border, so I took a taxi here with my friend as I can’t feed my family anymore,” 26-year-old Ouarda, from the neighbouring town of Tetouan, told AFP.

“I’m not scared — I’ll either die or I’ll cross,” the unemployed, divorced mother-of-two said.

One man drowned trying to swim across, Spanish officials said on Monday.

Videos posted on social media showed dozens of migrants — some wearing just beachwear but others clad in normal outdoor clothes — setting off from rocky beachheads.

“They stopped me from getting through, but I’m going to try again,” said one 26-year-old job-seeker.

The Spanish interior ministry said “immediate reinforcements of the civil guard presence and national police” would be sent to Ceuta, totalling 200 additional officers.

During the last weekend of April, around 100 migrants swam to Ceuta in groups of 20 to 30. Most were deported back to Morocco.

Ceuta and Melilla have the European Union’s only land borders with Africa, making them popular entry points for migrants seeking a better life in Europe.

Mohamed Benaissa, the head of the North Observatory for Human Rights in the Fnideq, said the bulk of those making it to the Spanish side were “minors, youths but also families, all of them Moroccan”.

The wave of arrivals comes at a time of diplomatic tension between Madrid and Rabat, after it emerged that Polisario Front leader Brahim Ghali arrived in northern Spain in mid-April and is being treated in hospital for Covid-19.

The Polisario Front has long fought for the independence of Western Sahara, a former Spanish colony that is mainly under Moroccan control.

Analysts had warned the spat could threaten cooperation between Madrid and Rabat in the fight against illegal immigration.

Benaissa said Monday’s influx “could be linked to the diplomatic crisis between Morocco and Spain”.

But Spanish Foreign Minister Arancha Gonzalez Laya said Rabiat had “assured” Madrid the huge influx was “not the result of the disagreement” with Rabat over the presence of Ghali at a Spanish hospital.