By Ian Talley 

WASHINGTON -- The Trump administration on Monday imposed counterterror sanctions on Iran's Ministry of Petroleum, the National Iranian Oil Company and its tanker subsidiary in a pre-election move that analysts say will make it more difficult for the pressure campaign to be reversed in the future.

The Treasury Department also blacklisted more than a dozen other major Iranian state energy firms and their subsidiaries, as well as top officials at the ministry and the firms, including the National Petrochemical Company and the National Iranian Oil Refining and Distribution Company.

The action comes amid concern within the administration that Democratic presidential candidate Joe Biden, who is leading in most battleground-state polls, could ease sanctions after promising on the campaign to re-engage with Iran, should he win next week's election.

The Treasury Department, in issuing the sanctions, said Iran's petroleum ministry, state oil giant NIOC, the National Iranian Tanker Company and the other blacklisted firms serve as critical financing sources for the Islamic Revolutionary Guard Corps' Quds Force, Iran's elite military unit designated by the U.S. as a terror group for its role in directing Tehran's proxies abroad.

"The regime in Iran uses the petroleum sector to fund the destabilizing activities of the IRGC-QF," said Treasury Secretary Steven Mnuchin, referring to the Quds Force.

Iran's mission to the United Nations didn't immediately respond to a request for comment.

Although the firms targeted by the U.S. on Monday were previously sanctioned, the new designations come under counterterror authorities, which analysts and former U.S. officials say are much more difficult to unwind than other types of sanctions. Besides the stigma of working with terror-designated entities and the political complications of rolling them back, such sanctions can carry tougher penalties for anyone caught transacting with the blacklisted firms.

Analysts say the designations put nearly all of Iran's petroleum sector under counterterror sanctions and should act as an additional deterrent for companies still doing business with Iran.

Write to Ian Talley at ian.talley@wsj.com

(END) Dow Jones Newswires

October 26, 2020 14:32 ET (18:32 GMT)