China's oil cooperation with Iran is transparent, open and reasonable, Foreign Ministry spokesman Hong Lei said on Thursday.

Hong made the comments at a daily news briefing in response to a question on whether the decline in China's crude oil imports from Iran is related to US sanctions against Iran.

"Our cooperation with Iran on crude oil is transparent, open, reasonable and commercial in nature. It does not run counter to UN resolutions or damage third party interests," Hong said.

China opposes sanctions imposed by any county on others based on its domestic law, the spokesman said.