China warned the United States on Thursday not to meddle in its trade relations with Iran after Washington expressed concern about a Chinese oil company's planned investment in an Iranian gas field. "We think this kind of cooperation and relationship is legitimate. Normal cooperation should not be interfered (with)," said Chinese Foreign Ministry spokesman Liu Jianchao. Asked if that meant Beijing believed the United States was interfering in its dealings with Iran, Liu said, "This is our position." The US government expressed concern to Beijing last month about a planned investment by state-owned Chinese oil company CNOOC Ltd. in Iran's Northern Pars gas field. Washington said major business dealings with Tehran were inappropriate at a time when Iran was defying UN resolutions over its nuclear program.