A Washington offshoot of Occupy Wall Street has won a green light to keep occupying until February 28, officials said Thursday, so long as it shares its space with a conservative group.

Occupy Washington DC in Freedom Plaza, which grew out of an anti-war protest in early October, had previously held a permit from the National Park Service -- which owns the square near the White House -- to remain until New Year's Eve.

"We will plan to go and speak to people and do actions, stuff like that," Sarah Hines of Occupation Washington DC told AFP, confirming the permit extension and the encampment's plans to widen the reach of its protests.

But the tent city, housing several dozen activists, will be rubbing shoulders with the free-market National Center for Public Policy Research, which has a permit for lunchtime rallies in Freedom Plaza from February 12.

"They have to share space, or make space, when others want to use Freedom Plaza," said National Park Service spokesman Bill Line, adding that Occupy Washington DC has done just that on previous occasions.

Spokesmen for the conservative center -- which campaigns for "a strong national defense (and) free market solutions to today's public policy problems" -- could not be reached for comment.

Washington's other open-ended protest, Occupy DC, pitched camp on October 1 in McPherson Square, in the heart of the K Street lobbying district, where by federal law no permit is needed for gatherings of fewer than 500 people.

A third group, Occupy Congress, has meanwhile applied for a permit to demonstrate in conjunction with Occupy DC on the National Mall on January 17, the day Congress returns from its winter break.

Washington is host to the longest-running occupations in the United States after police shut down protests in other cities, including the original Occupy Wall Street in New York City on November 15.

In a year-end interview, Mayor Vincent Gray -- a veteran activist who was himself arrested in April at a Capitol Hill protest demanding statehood for the District of Columbia -- expressed frustration with the Occupy movement.

"What is the desired outcome here? Where are you trying to get to?" Gray asked in The Washington Post. "You see signs that read, 'End corporate rule.' Well, how do you do that?"

Neighborhood shops, restaurants and office building tenants have also voiced impatience.

The most serious incident in Washington came on December 7, when police arrested 62 occupiers for blocking a K Street intersection during a labor union protest in the US capital.

Three days earlier, police raided McPherson Square and pulled down an "occubarn" that went up the day before with no prior notice. The wood-frame structure was meant to be a meeting place during the winter months.