Tehran said Tuesday it was canceling a $2.5 billion deal with China National Petroleum Corp. for the development of a giant Iranian oil field, as privileged ties between both nations face mounting challenges. China had stepped in after Western oil companies pulled out of Iran following a European ban on investing in the Islamic Republic. But an interim nuclear deal between Iran and six world powers has led the Islamic Republic to be more assertive toward Beijing, which some officials say has unduly taken advantage of international sanctions. Following repeated delays, “termination of the company’s South Azadegan oil field development project has been issued,” Iran’s oil ministry website Shana quoted Roknoddin Javadi, the managing director of the National Iranian Oil Co., as saying. CNPC didn’t return a request for comment. —Wayne Ma in Beijing contributed t this article