Reports are surfacing that the Libyan government is now preventing foreign migrant workers in the country from leaving.

While it is believed that about 180,000 foreigners have already escaped the strife-torn nation, many untold thousands remain trapped.

Most worrying, the number of foreigners cross into Tunisia has declined dramatically -- from about 10,000-15,000 per day earlier this week to less than 2,000 on Thursday, according to the UK paper Guardian.

The United Nations’ main agency for refugees expressed its concern in a statement.

The border on the Libyan side is now manned by heavily armed pro-government forces, it said. From those that did manage to cross the border, we have heard that mobile phones and cameras were being confiscated en route. Many people appear to be frightened and are unwilling to speak.

Satellite images acquired by the UN apparently reveal the presence of large numbers of people sitting idly on the Libya side of the border with Tunisia.

It's an artificial and abrupt stop. We have no idea why, but we're trying to find out, said Andrew Mitchell, the British international development secretary. “The [sudden] break in numbers doesn't feel right.

Meanwhile, Tunisian authorities are overwhelmed and unable to cope with the needs of the thousands of people who have already crossed into the country.

It is believed that most Egyptians in Libya have been able to go back home – the remainder are described as from across the world, including Vietnam, Bangladesh, Nigerians, Malians and Ghanaians.