Norwegian state oil firm Statoil said it could face penalties from the United States in connection with the company's operations in Iran and is risking losing 171 million barrels of oil reserves in an "incredible" case in Venezuela.

In an annual report filed with the US Securities and Exchange Commission (SEC), published on Tuesday, Statoil stressed that an agreement executed in 2002 to help develop the South Pars gas project in Iran could be deemed a violation of the Iran Sanctions Act (ISA) adopted by the US, Reuters said.

Statoil also pointed to potential losses in Venezuela, where President Hugo Chávez' nationalization plans are endangering foreign oil companies' operations.

Statoil holds a 15 percent share in the heavy-crude oil Sincor joint venture with French Total and the Venezuelan state-owned Pdvsa.  "The possible migration from partnership to a joint company and the resulting possible reduction in Statoil share may affect our future recognition of proved reserves. The maximum adverse impact on proved reserves is currently estimated to 171 million barrels of oil," the company said in the report.

According to the firm, transfer of operations is to be completed by April 30, 2007, and the law provides for a four-month period to agree on the terms and conditions for participation in the new joint companies.