Soona Samsami, the US representative of the National Council of Resistance of Iran, a parliament in exile whose main member is the People's Mujahedeen, said the US policy of engagement with Iran had failed and urged regime change.
"It is now time to direct all efforts towards democratic change in Iran," she said in remarks at the opening. "The United States must stand with the Iranian people as they stand for liberty."
The People's Mujahedeen, also known as the MEK, had been listed by the State Department as a "terrorist organization" since 1997, but the administration of President Barack Obama lifted the designation in September.
The group was founded in 1965 with the aim of overthrowing the Shah of Iran, but after the country's Islamic revolution in 1979 it took up arms against the Islamic regime, operating from bases in Iraq.
More than 3,000 members of the group remain confined to two camps in Iraq.
The MEK says it has now laid down its arms and is working to overthrow the Tehran regime through peaceful means.
Samsami said Tehran's leaders were "focused on eliminating its organized opposition, thousands of whose members are in Camp Ashraf and Camp Liberty.
"It is fully aware that the MEK in general and the residents of Ashraf and Liberty in particular will play a decisive role in any development inside the country," she said.
Jones called the MEK "a very important movement, which will hopefully lead someday to the restoration of democracy and the rule of law, in the wonderful country of Iran, where the people deserve so much better than they're getting."
Bolton said the MEK's delisting came at a critical time with nuclear proliferation threats from North Korea and Iran, and praised the opposition group for calling for a nuclear-free Iran.
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