WASHINGTON (AP) — The federal government is escalating security around the country in preparation for the 10th anniversary of the 9/11 terrorist attacks and conducting confidential briefings with state and local law enforcement organizations. But officials say there is no specific indication that a terror plot against the U.S. is under way.

Americans can expect more security at airports, mass transit stations, U.S. borders, government buildings and major athletic events over the next month, said an intelligence official who spoke anonymously to discuss sensitive security matters.

The FBI and Homeland Security Department have been briefing state and local law enforcement agencies on potential terror threats to the U.S. and ways to increase security in their communities. The briefings are routine, and security has been enhanced for other major events in the past decade. But the significance of the 10-year anniversary of the worst terror attacks on U.S. soil is not lost on security officials, who fear that someone with terrorist sympathies might see 9/11 as an opportunity to make a statement.

"It's been a long buildup as we approach the anniversary of 9/11," said Sean Duggan, assistant chief at the Scottsdale, Ariz., Police Department. Duggan said his department gets daily updates from the FBI and Homeland Security Department. But over the past two months, the focus has been on the 10th anniversary of the terror hijackings.

"We know this is a significant date," Duggan said. "Other than taking physical precautions, we have not been briefed on any specific threat other than the obvious — knowing what this date means in our history."

Events are planned around the country to commemorate the nearly 3,000 people killed in the 2001 attacks.

"While there is currently no specific or credible threat, appropriate and prudent security measures are ready to detect and prevent plots against the United States should they emerge," Homeland Security Department spokesman Matt Chandler said.

President Barack Obama said earlier this month that the threat of a plot by a lone terrorist is particularly troublesome.

"The risk that we're especially concerned over right now is the lone-wolf terrorist, somebody with a single weapon being able to carry out wide-scale massacres of the sort that we saw in Norway recently," Obama said.

In July, 69 people at a youth camp in Norway were shot to death. Authorities said a white supremacist carried out the attack with the purpose of saving Norway and the rest of Europe from Muslims and multiculturalism.

"You know, when you've got one person who is deranged or driven by a hateful ideology, they can do a lot of damage, and it's a lot harder to trace those lone-wolf operators," Obama said.

Some of the first information gleaned from Osama bin Laden's compound after he was killed in May indicated that, as recently as February 2010, al-Qaida considered plans to attack the U.S. on the 10th anniversary of the 9/11 attacks. But counterterrorism officials said they believe the planning never got beyond the initial phase and had no recent intelligence pointing to an active plot.

One idea outlined in handwritten notes pulled from bin Laden's Pakistani hideout was to tamper with an unspecified U.S. rail track so that a train would fall off the track at a valley or a bridge, according to a joint FBI and Homeland Security Department bulletin to law enforcement officials around the country. The al-Qaida planners noted that if they attacked a train by tilting it, the plan would only succeed once because the tilting would be spotted the next time.

Even before the raid, intelligence officials for years have warned that al-Qaida is interested in attacking major U.S. cities on holidays, anniversaries — including the anniversary of the 9/11 attacks — and other dates that are uniquely American.

White House spokesman Clark Stevens, asked about the briefings, said the president's homeland security and counterterrorism adviser, John Brennan, has had senior-level meetings over the past four months about threats to the U.S. and appropriate responses leading up to the anniversary.

"These senior-level reviews of our security posture will continue through the 9/11 anniversary and beyond, in order to ensure the federal government remains fully prepared to take whatever steps are necessary to mitigate any potential attacks," Stevens said in a statement.