Hundreds of migrants are missing feared drowned after 165 people were rescued from a capsized fishing boat in the Mediterranean.
Seventeen bodies were initially recovered from the sea, with the death toll expected to rise after the craft with at least 600 people on board overturned north-west of the Libyan capital Tripoli.
Irish authorities confirmed the death toll after the Irish Navy vessel the LE Niamh was sent to the scene at 8am following distress calls.
Simon Coveney, Ireland's Defence Minister, said the death toll is significant and likely to rise.
"As the operation is currently ongoing, with all personnel fully engaged in the rescue, it is difficult to ascertain full details on the scale of the incident," he said.
"However I understand that the fishing vessel capsized and that the loss of life is likely to be significant. The crew of the Niamh are working flat out with their counterparts to rescue as many as possible."
The LE Niamh was involved in the search and rescue mission - feared to be the worst since April when 800 migrants died in a capsize incident - along with Italian naval vessels, the Medecins Sans Frontieres vessel MV Dignity I, crews from the Migrant Offshore Aid Station (Moas), based out of Malta and a number of helicopters.
Life rafts were being dropped to the sea while rigid inflatables were also being sent.
"Our thoughts and prayers are with all those who have lost their lives, the survivors and the rescuers for whom this is an extremely difficult operation," the Minister said.
The incident is understood to have happened about 25 miles off the Libyan coast after the boat left from the city of Zuwara in the north-west of the country early this morning.
The International Organisation for Migration (IOM) said they had received reports that as many as 700 migrants had been on board.
The agency said it was receiving reports of a "significant number" of casualties.
Only days ago the IOM warned the death toll of migrants trying to cross the Mediterranean this year had reached 2,000 compared with 3,279 for the whole of 2014.
The crew of the Dignity I said there had been "many deaths".
"According to information currently available, there could have been up to 700 people on board at the time of the incident," a spokesman said.
"MSF can confirm that there are many confirmed deaths at the scene but cannot provide additional information at the moment."