At least 172 people are believed to have drowned in three different shipwrecks in the central Mediterranean Sea, and the number of drowning in the world's deadliest crossing has more than doubled this year, the International Organization for Migration (IOM) said Friday.

"Over the past three days, we have received reports that there were at least three boats" that have sunk "in the central Mediterranean," said IOM spokeswoman Safa Msehli at a UN press briefing.

She noted that the IOM was quoting tolls given by NGOs operating rescue ships in the area.

On one of the boats, there were 130 people aboard. A second was carrying two people.

"There are further reports of a third boat carrying up to 40 people. We have no news on this boat," said IOM's Msehli.

She said the boat has been at sea for three days, and they fear that the worst has happened given the status of these boats.

"This actually brings the death toll in the central Mediterranean alone to close to 500 people, which is almost three times as many as the death toll in the same period of last year," said Msehli.

"In the Mediterranean as a whole, there have been 523 recorded deaths. If we add the numbers from yesterday, that's 650 recorded deaths."

She said that in the central Mediterranean alone, "which remains the deadliest sea crossing," there were as of Thursday close to 500 deaths, compared to 149 in the same period last year.

"So nearly a threefold increase in the number of recorded deaths," said the IOM spokeswoman.

She added: "But let me also be clear that our ability to monitor deaths in the central Mediterranean especially has been reduced drastically due to the absence of states' search and rescue vessels and the lack of information."

The reports of the shipwreck were first shared with the IOM by the NGOs SOS Mediterranee and Ocean Viking, which have rescue vessels in the Mediterranean./aa