The United States embassy in Cambodia has fired 32 people after they were allegedly caught sharing pornographic material in a non-official chat group, several sources familiar with the matter said on Friday.

Four sources told Reuters that pornographic videos and photographs, including some featuring people under the age of 18, were shared in a Facebook Messenger chat group.

Some of the images were seen by the wife of an embassy worker who reported the incident to an official at the embassy. The matter was then forwarded to the Federal Bureau of Investigation (FBI), the sources said.

"They had their identification cards taken and some of their phones checked," a former US embassy staff member told Reuters on condition of anonymity.

He said the 32 embassy workers included Cambodians and Cambodian-Americans. Many were guards and some were clerical staff. There were no diplomats among them, they said.

Two of the sources, both of whom work at the embassy, confirmed the dismissals.

The dismissals come at a time of tension between Cambodia and the United States over US criticism of a crackdown on dissent by long-serving Prime Minister Hun Sen, and his anger over what he says have been US efforts to undermine his rule.

The US has denied interfering in Cambodian politics. The Cambodian government has not commented on the dismissals.