Despite travel ban to Afghanistan by the Philippine government, as much as 4,000 undocumented Filipinos are working in the western Asian state, labor and diplomatic sources said on Friday.

These Filipinos, according to sources, are hired by contractors of U.S. firms operating in Afghanistan and have managed to slip through the country via Dubai, United Arab Emirates.

The salary of these workers, sources said, could fetch up to 10, 000 U.S. dollars a month.

Manila has no embassy in Afghanistan, making it difficult for Philippine authorities to monitor the entry and movement of Filipinos there.

"We can not do anything. They keep on coming because of the high pay and we can not match the salaries they're getting there here in the Philippines," a labor official said.

Before the 2007 deployment ban, around 1,000 Filipinos have been working and residing there, including those who work for United Nations attached agencies.

The Philippines stopped sending workers to Afghanistan following the U.S.-led invasion of the western Asian state and the unstable security condition in the country. The Philippines also prohibits travel to Nigeria, Iraq, Lebanon and Jordan.

Earlier this week, six undocumented Filipinos perished in a cargo plane crash outside of capital Kabul. In a similar incident in July 2009, a civilian helicopter had problems taking off at the Khandahar airfield in Afghanistan and crashed, killing all its passengers including 10 Filipino workers.

Currently, the Philippine government is in a dilemma on how to provide protection to the increasing entry of Filipinos in Afghanistan with the lingering security threats.

"It's a challenge for us," a Filipino diplomat said. "We do not know how to stop the entry of our workers there."

But the government is optimistic that the a recent U.S. order to pull out all foreign workers from states imposing a travel ban to Afghanistan would hopefully reduce Filipino workers in that country.

On Sept. 17, the U.S. Central Command advised all contractors in Afghanistan to remove third country nationals, including Filipinos, from the jobsites upon the termination of their contracts this year and to repatriate them to their country of origin.

Contractors who will violate the U.S. directive would result to contract termination or debarment from future US government contracts.