Italian authorities have rescued more than 11,000 migrants making the often deadly voyage from North Africa in the past six days, with hundreds more expected Friday, the coastguard said.
The migrant wave has swelled in recent days on the back of the worsening security situation in Libya -- the staging post for most of the crossings -- as well as milder spring weather. Alarm and outrage is growing in Europe as the death toll mounts in capsizes and sinkings of unseaworthy craft used by ruthless people smugglers, with many of them taking advantage of the lawlessness in Libya, which has a long Mediterranean coastline.
"It's a sea, not a cemetery," Italian Prime Minister Matteo Renzi said Friday in Washington. "The problem in this moment is the situation on the ground in Libya."
Aid workers said Friday a woman was found dead and 15 other people, including a six-month baby, were found injured on an inflatable dinghy carrying 90 people that had been adrift for two days.
The woman had been taken onboard despite suffering serious burns in a gas canister blast in a Libyan camp housing migrants waiting to be smuggled into Europe, the UN's refugee agency said.
More than 300 migrants were rescued on another stricken boat Friday, among them 45 women and 23 children, rescuers said.
About 400 other migrants rescued in the Aegean Sea in recent days arrived Friday at the Port of Piraeus in Athens.
- 'Christian persecution' -
Meanwhile, prosecutors in the Sicilian port of Palermo asked a court to remand in custody 15 migrants accused of throwing a dozen Christian passengers overboard after a row during a crossing from Libya.
Survivors told Italian police that a group of Muslim migrants attacked a group of Christians in a dispute over religion and that those who survived had "forcefully resisting attempts to drown them".
Investigators interrogated the 15 accused -- said by police to be from Ivory Coast, Senegal and Mali -- on Thursday night.
The 12 victims were from Ghana and Nigeria, according to the police.
Cardinal Antonio Maria Veglio, speaking for the Vatican, lambasted the deaths as an "act that must be condemned absolutely: Killing a fellow traveller to save your life while seeking a better life is very sad."
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"You cannot condemn everyone, we have to distinguish groups of fanatics, though it is a horrible fact and it is undeniable that there is persecution against Christians," he told news site Vatican Insider.
The case caused shock in Italy where investigators said that while fights on board were common, the violence suffered by migrants was usually caused by "unscrupulous traffickers and smugglers who pack them into unseaworthy vessels" -- not other passengers.
"The religious clash which is believed to have claimed lives is a really worrisome departure," Palermo's prosecutor general Francesco Lo Voi told the Italian daily La Repubblica.
Archbishop Giancarlo Perego of a Catholic organisation that helps immigrants, said the killings, if confirmed by the investigation, would be "a tragedy within a tragedy".
- Italian trawler recaptured -
The head of the Union of Islamic Communities in Italy, Ezzedin el-Zir, warned against blaming the incident on Islam or on migration.
"We mustn't give into political and electoral propaganda," he said, alluding to remarks by the anti-immigrant Northern League party, which has called on local authorities to refuse Rome's demands to take in migrants.
Meanwhile, in another sign of growing jitters over the chaos in war-torn Libya, the Italian navy rushed to the rescue of an Italian fishing trawler that was seized by gunmen off the north African state.
An Italian navy spokesman said the Airone had been seized by a tug apparently belonging to the Libyan security forces, 90 kilometres (55 miles) northwest of Misrata.
"We can confirm that navy personnel... have boarded an Italian ship and have taken control," he added.
The Libyan authorities frequently detain Italian trawlers they accuse of fishing illegally in their waters, but they usually let them go after negotiations.
The International Organization for Migration estimates the migrant death toll at 900 since January, a nearly tenfold increase on the same period last year.
Rights groups say migrants are so desperate that they go even when told about the danger of the crossing.
Conditions in migrant holding camps in Libya are particularly harsh, with many of those who make it to Europe reporting beatings by smugglers and food deprivation.