With oil companies waiting in the wings, the supreme leader of Iran said there will be no foothold for the United States in a post-sanctions era.

Testing a veto threat from the White House, Republicans and some Democrats in the U.S. House and Senate are expected to vote against the July nuclear agreement reached between Iran and the five permanent members of the U.N. Security Council, plus Germany. That deal could ease sanctions pressure on Iran, a top producer in the Organization of Petroleum Exporting Countries.

With the deal in hand, global energy companies from Royal Dutch Shell to Italy's Eni have reviewed potential business opportunities in Iran. Iranian Supreme Leader Ali Khamenei said Monday he had lingering questions about the U.S. commitment to the deal.

"With the nuclear deal still undecided by both Congress and our Parliament, no such U.S. lead and foothold inside the country would be possible," he said.

Iranian Oil Minister Bijan Zangeneh last week said the finishing touches were put on terms for potential new oil contracts in the post-sanctions era. Though European countries are moving quickly, and "all international companies" are welcome, the minister said there's been no formal interest expressed from U.S. energy companies.

Most international oil companies said they're still minding sanctions targeting Iran's energy sector.

Iran reported to OPEC oil production for July at 3.13 million bpd, an increase of six tenths of a percent from the previous month. Crude oil production in pre-sanctions era ran was around 3.6 million bpd.

Crude oil exports, meanwhile, are limited to around 1 million barrels per day and to six nations under the terms of existing sanctions.