Washington: Energy giants Total SA, Royal Dutch Shell, Statoil and Eni have pledged to end their investments in Iran.

The pledges fall in line with tough new energy and financial measures the US Congress imposed on Iran in June, which came atop UN Security Council sanctions imposed earlier the same month to curb Iran's nuclear ambitions.

"I am pleased to announce that we have received commitments from four international energy firms to terminate their investments and avoid any new activity in Iran's energy sector," Deputy Secretary of State James Steinberg said, calling the move "a significant setback to Iran."

Steinberg said the move makes the companies eligible to avoid US sanctions.

‘Provided assurance'

The companies "have provided assurance to us that they have stopped," or taken steps to stop business with Iran, he said.

"However, some international oil companies have not yet committed to any new activities in Iran's petroleum sector. And for this reason the State Department is launching investigations into those companies," he said.

He would not identify these firms or say how many there are. Two senators urged Secretary of State Hillary Clinton on Tuesday to ensure that the administration punish Chinese and Turkish firms reportedly providing Iran with refined petroleum products.

Steinberg also said the State Department decided to impose sanctions on Naftiran Intertrade Company, a Swiss-based subsidiary of Iran's national oil company, for its involvment in Iran's energy sector.