EU patrol vessels in the Mediterranean are putting lives at risk by operating too far from the Libyan coast where migrants are embarking on the perilous voyage to Europe, the head of a rescue charity said today.

Growing numbers of migrants are attempting the crossing in flimsy, overcrowded boats as the spring weather improves. Nearly 9,000, mostly Africans, were rescued over the long Easter weekend, UN aid agencies said.

'The further they (Frontex) stay away, the more people will die': Chris Catrambone

"Europe needs to rescue people because it cannot allow them to die at its own back door," said Chris Catrambone, an American businessman who co-founded the Migrant Offshore Aid Station (MOAS), with his Italian wife Regina in 2014.

He was speaking by telephone from the MOAS rescue vessel Phoenix, which after a frantic weekend's activity was heading slowly towards Sicily with 463 migrants on board, including 170 women and children, and seven dead bodies recovered from the sea.

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The crossing from Libya to Italy is now the main migrant route into Europe. More than 181,000 came to shore in Italy last year, and arrivals this year are up about a third on the same period of 2016.

Some 850 are estimated to have died so far in 2017. That is fuelling a dispute over whether laying on more rescue vessels, and patrolling closer to Libya, is encouraging the flow of migrants and boosting the profits of people-smugglers.

Since Italy abandoned its search-and-rescue mission in 2014, the European Union's border control agency Frontex has taken over patrolling the Mediterranean, but its ships remain well clear of the Libyan coast.

Both Frontex and a Sicilian prosecutor have said NGOs should not be working so close to Libya because they make it too easy for migrants to come to Europe, adding that some NGOs may be in contact with smugglers.

Frontex said yesterday it had rescued more than 1,400 people over the weekend.

"Smugglers are taking advantage of the proximity" of the NGOs by using more unsafe boats and packing them even tighter, the agency said in an email to Reuters on Tuesday.

While the NGO boats tend to hover just outside of Libyan territorial waters that end 12 nautical miles from the coast, Frontex vessels patrol much further north and can take a half-day or more to reach the boats in distress.

Catrambone said the only question at sea is life or death.

"The priority needs to be saving lives, not patrolling a make-believe border. The further they (Frontex) stay away, the more people will die. Saying there is a pull factor is just ignorance. It's avoiding responsibility," he said.

All of about a dozen NGOs operating in the Mediterranean have taken similar positions in recent weeks.

"How many lives could have been saved in the last two years if the #EU had conducted a proactive search and rescue operation? #WhereIsFRONTEX," tweeted one of the groups, Doctors without Borders (MSF), on Sunday.

On Tuesday, MSF said it was being sent 164 miles to respond to a rescue call. "Where are #EU boats?" it tweeted.