Mayor Vincent C. Gray said Friday that the D.C. police department is requiring officers to work 12-hour shifts and operate under a restricted leave policy as city officials try to protect the nation’s capital under “credible and specific but unconfirmed threats.”

Gray (D) repeated an announcement he made late Thursday about the potential threats to the District and New York City surrounding the 10th anniversary of the terrorist attacks of Sept. 11, 2001.

D.C. police and other law enforcement agencies had already put a plan in place that Chief Cathy L. Lanier had described as a decade in the making. But the new potential threats, which federal officials shared with local leaders, have spurred the city to increase security, Gray said in a news release.

“We take these threats seriously — as we do all threats to our city — and citizens should know we are taking all the appropriate steps to ensure their safety,” Gray said.

Since the mayor was warned of potential safety threats, the city’s public safety team has been in “constant contact with ... federal counterparts, including the U.S. Department of Homeland Security, the FBI, the Federal Emergency Management Agency, the Joint Terrorism Task Force and the Joint Forces Headquarters,” Gray said. “We are working closely with them to share information and coordinate our efforts.”

Gray said residents will notice more police officers, and the city is prepared to take a higher volume of calls on 911 and 311.

Later in the day, Gray and Lanier briefed members of the D.C. Council on the threat.

Lanier said she planned to inform the council of the city's stepped-up security plans for the weekend and outline the need for residents to remain vigilant.

But because council members do not have security clearances, the briefing did not include information that was not readily available to the public, officials said.

"I think they need to feel comfortable we are doing everything we can to keep residents safe," Lanier said.

In his news release, Gray outlined specific instances when citizens should contact law enforcement:

* Vehicles parked illegally in front of entrances to venues – such as government buildings, restaurants, transit stations, theaters, sports arenas, convention halls and houses of worship — that host large groups of people.

* Vehicles that appear overloaded or have strange odors coming from them.

* People acting very suspicious or nervous for no apparent reason.

* Briefcases, luggage, backpacks or packages left unattended in public places and on public transit.

* Intruders in secure areas where they are not supposed to be.

Staff writer Tim Craig contributed to this report.