The letter was in response to a Securities and Exchange Commission's Office of Global Security Risk request that asked whether HP's products were sold in countries where they would be subject to U.S. sanctions.

HP had requested confidentiality, even as it insisted that it had authorized the sale of its products to Syria in its October 9 response.

Instead, HP said Italian surveillance company Area SpA had likely obtained its products from an HP partner that was unaware of their ultimate destination.

In another October 9 letter to the agency, HP said that it had ended its contract with Area SpA in April.

Calls to HP seeking further comment were unanswered as were calls to Area SpA.

HP's overseas subsidiaries ended sales of printers and related supplies to third-party distributors and resellers with customers in Iran in in early 2009, the company wrote.

But because its products are often sold by others through indirect channels without its knowledge or consent, "it is always possible that products may be diverted to Iran or Syria after being sold to channel partners, such as distributors and resellers," HP said.

Reuters has documented how banned computer equipment from U.S. companies has made its way to Iran's largest telecom firm through China-based ZTE.

Networking equipment maker Cisco Systems has since cut its ties to ZTE.

HP said in both letters that it would continue to work with ZTE, but that it had conducted an internal investigation relating to an alleged sale of its products to MTN Irancell, Iran's second largest mobile carrier.

HP is eager to avoid more negative publicity after surprising the market on Tuesday with an $8.8 billion write-down on its $11.1 billion acquisition of software group Autonomy accusing the British company of improper accounting to inflate sales.

Autonomy has denied any wrongdoing.

(Reporting by Nicola Leske; Editing by Leslie Gevirtz)

By Nicola Leske