Boat with 500 immigrantsincluding a newborn and pregnant women, is missing in the central Mediterranean, as two humanitarian organizations said today.

Alarm Phone, a humanitarian organization that monitors calls for help on boats carrying migrants, says it lost contact with the vessel on Wednesday morning.

At that moment, the boat sailed unruly, as his engine was not working amid rough seas some 320 kilometers north of the Libyan port of Benghazi and more than 400 kilometers away from Malta or Sicily.

The Italian NGO Emergency said yesterday that the Life Support ship as well as the Ocean Viking, another aid vessel, searched without success for the missing boat for 24 hours but found no sign of a wreck.

A spokesman for Emergency reported today that the investigation continues, adding that the migrants may have been picked up by another vessel or managed to repair the engine and continue their journey to Sicily.

The Italian Coast Guard reported the rescue yesterday 423 and 671 immigrants in two separate operations in waters where search and rescue is under Italian jurisdiction, while Alarm Phone said they were not connected to the missing vessel. The Italian coastguard had no immediate comment.

In a separate incident, the German humanitarian organization SOS Humanity reported that 27 migrants were picked up at sea by an oil tanker and returned illegally to Libya.

Under humanitarian law, migrants cannot be forcibly returned to countries where they are at risk of serious ill-treatment, and widespread abuse of migrants has been recorded in Libya.

European governments are increasingly adopting hard line on immigration, including Italy, which is facing an increase in arrivals by sea. Over 47,000 arrivals have been recorded since the beginning of the year, compared to around 18,000 in the corresponding period last year.