'They left them to die': Activists seek criminal probe into migrant deaths off Libya

Their protest came as rights groups expressed growing concern about the plight of migrants attempting the dangerous Mediterranean crossing - and accused officials in several countries of blocking their efforts to help them.

In a tweet Claus-Peter Reisch, founder of the German group Mission Lifeline, accused the EU agencies Frontex and Eunavfor Med, which police the bloc's border and coastguard activities, of "crimes against humanity" and called on "the International Criminal Court (ICC) to investigate".

Axel Steier, a spokesman for the group, told AFP that both agencies "have military vessels, satellites, reconnaissance planes covering all of this zone".

"They had the means to see that these refugees were in distress. But they did nothing, they left them to die," he added. "That's called a crime."

A group of 25 migrants left Sabratha, 70 kilometres (44 miles) west of Tripoli, in a bid to reach the Italian coast, said the Libyan Red Cross.

But the currents meant that they drifted for 11 days without food or water, capsizing off Misrata, 270 kilometres further east, and washing up on a beach Monday evening.

There were only 10 survivors, two of them women, and all of them were suffering severe dehydration when they were found.

Others aid agencies on Wednesday also denounced the lack of help for migrants attempting the perilous Mediterranean crossing to Europe.

Doctors Without Borders (MSF) tweeted of "increasingly alarming" reports confirming its own observations: "search & #rescue capacity is insufficient, and boats in distress are being ignored or refused help".

"During this time, civilian rescue vessels are prevented from carrying out their mission by targeted political attacks," said a statement from French migrant rights group SOS Mediterranee.

Their vessel the Aquarius, run jointly with MSF, is currently stuck in the French Mediterranean port of Marseille after Manama revoked its flag rights, which means it cannot legally set sail.

Mission Lifeline's main vessel, Lifeline, is itself stranded at the Maltese port of Valetta, also for legal reasons.

According to the latest figures from the International Organization for Migration (IOM) released Tuesday, 1,285 people have died trying to cross the Central Mediterranean since the beginning of the year - despite a significant drop in the numbers attempting the crossing.