Pro-Camp Ashraf protesters outside the White House on December 12, 2011 in Washington, D.C. (Ricky Carioti/WASHINGTON POST)

The National Council of Resistance of Iran, an umbrella group that included an armed wing (Mujahedin-e Khalq, or MEK), opened its new Washington, D.C. office Thursday.

The group, fierce opponents of the regime in Tehran — and which the Iranians brand a violent cult — had been on the State Department’s list of foreign terrorist organizations since 1997. The NCRI hasn’t been able to operate in this country since 2003.

There had been some 3,000-plus MEK in Camp Ashraf in Iraq near the Iranian border. The MEK turned over its weapons to the Army — and has rejected violence, an NCRI official told us. But pressure from Iran led the Iraqis to close the camp recently and move the MEK closer to the capital — where they get hammered regularly by mortar fire. (The group’s leadership is based in Paris.)

A lengthy lobbying and legal campaign — backed by folks such as former U.N. ambassador John Bolton, Rep. Dana Rohrabacher, presidential candidates Newt Gingrich (R), Rudy Giuliani (R) and Howard Dean (D) and former Pennsylvania governor Ed Rendell — eventually forced the State Department to remove the organization from the terrorist sponsor list.

NCRI officials noted that Bolton, former Obama National Security Adviser Jim Jones, former Rep. Patrick Kennedy (D-R.I.) and other backers attended the opening of the office of what’s now styled as “Iran’s Parliament-in-exile.”