Foreign contractors working in the Iranian energy sector need to stay committed to their obligations or face expulsion, a development official said Tuesday.

Abdorreza Haji Hosseinnejad, the director of Iran's Petroleum Engineering and Development Co., said contractors need to respect the terms of their contracts with the Iranian government.

"Unjustified delays, refusal to respect legal obligations in the development of fields particularly joint fields will lead to their removal," he said.

Iran in early May canceled a contract with China National Petroleum Corp. for work at South Azadegan oil field, a 40-billion barrel field straddling the Iran-Iraq border. Awarded the contract in 2009, Iran says CNPC was dragging its feet on the project.

Iranian Oil Minister Bijan Zanganeh had said Chinese companies were still welcome to participate in Iran's energy sector despite issues with CNPC, though the development official said all parties working on joint field development need to work to make up for any unnecessary delays

Iranian President Hassan Rouhani left Tuesday for Beijing to attend a two-day summit of Asian nations.

Iran estimates the South Azadegan oil field holds more than 40 billion barrels of oil.