A US firm specializing in Internet censoring equipment on Friday confirmed that Syria was using its products to block web activity, amid a brutal crackdown on anti-regime protests.

Northern California-based Blue Coat Systems told AFP that Internet filtering equipment sold to Iraq's communications ministry has mysteriously been put to use in Syria but insisted it did not know how the equipment changed hands.

The United States bars selling any such equipment to Syria.

"The evidence points to it being in Syria," a Blue Coat official said, referring to analysis of data logs and computer address numbers from Syria's Internet posted by 'hactivists.'

"Since we didn't sell it there, we don't know the particulars," said the official, who asked not to be named due to the sensitivity of the matter.

The official said that it appears that at least 13 of the 14 Web censoring "appliances" shipped to Iraq -- which combine computer hardware and software -- are being used in Syria.

That would be enough equipment to effectively curb Internet traffic in that country, according to the company, which said the equipment was shipped to Dubai for delivery to the Iraqi government.

Paperwork marking the chain of custody gave the impression the Internet filtering gear had been delivered to the intended customer, according to the company.

The United Nations estimates that more than 3,000 people, mostly civilians, have been killed in the bloody repression of anti-regime protests that have rocked Syria since mid-March.