Capitol Police officials have stepped up the department’s security presence on Capitol Hill in response to intelligence indicating the increased possibility of an al-Qaida terrorist attack on Congress sometime between now and Sept. 11.

The August-to-Sept. 11 time frame was confirmed by a Capitol Police source who said Congressional security officials were recently made aware of the potential threat by federal anti-terrorism authorities. The Capitol Police department has a liaison from the Homeland Security Department working in its Capitol Hill command center.

On Thursday afternoon, Senate Sergeant-at-Arms Terrance Gainer, who currently serves as chairman of the Capitol Police Board, acknowledged the noticeable increase in Capitol Police presence on the Hill but declined to discuss any specific threat or dates.

“Given the world situation and recently released snippet from al-Qaida threatening to attack Washington, we’re just being a tad more vigilant if that’s possible,” Gainer said. “Although, if you’re ready for a four-alarm fire at any time, it’s hard to be more vigilant.”

Gainer said Police Chief Phillip Morse and his command staff were “continuing to pump [the officers] up and reinforcing the need to be very vigilant. They are well-linked-in with the other law enforcement agencies in the city.”

When asked about the significance of the approaching sixth anniversary of Sept. 11, 2001, Gainer, the former chief of the Capitol Police, said, “The interesting thing with any dates is that analysts tell us that Americans tend to be much more oriented toward anniversaries and the jihadists seem to be less so. I’ve seen over the years where we concentrate on dates and the analysts say, ‘Don’t get wrapped up in dates because our terrorist jihadist enemies bide their time.’”

Rep. Zach Wamp (R-Tenn.), who helps oversee Capitol campus issues as ranking member of the House Appropriations Subcommittee on the Legislative Branch, would only say Thursday that “the leaders of the committees of jurisdiction have been briefed on threats to the Capitol.”

Without mentioning a specific threat to the Capitol, Senate Minority Whip Trent Lott (R-Miss.) ominously advised Thursday that Congress needed to pass changes to terrorist surveillance laws before leaving for the August recess and warned that otherwise “the disaster could be on our doorstep.”

When asked if people should leave Washington, D.C., during the month of August, Lott responded, “I think it would be good to leave town in August, and it would probably be good to stay out until September the 12th.”

A Capitol Police spokeswoman declined to discuss how specific or credible the current threat is, and would only say, “we remain vigilant at all times.”

Emily Pierce and John Stanton contributed to this report.