Norwegian energy group Statoil said Wednesday it was selling some of its oil assets in the United States to China's state-owned CNOOC, marking the first step by a Chinese energy major into the US market.

"On 29 October Statoil signed a farm down agreement with the Chinese company CNOOC (China National Offshore Oil Corporation) involving a number of Statoil's leases in Gulf of Mexico," Statoil said in a third quarter earnings statement.

Statoil did not give further details about the operation but spokesman Kai Nielsen told AFP that the size of the deal was "very small."

In 2005, CNOOC was forced to cancel an 18.5-billion-dollar (12.4-billion-euro) deal with US company Unocal following domestic political opposition in the United States over the sale of strategic assets to China.