Local and federal law enforcement agencies said Monday that the nation must remain vigilant against potential reprisals following the U.S. killing of Osama bin Laden.

To enhance security locally, the U.S. Department of Homeland Security announced the awarding of $4 million to improve security and communications along the Canadian border.

Federal law enforcement and security agencies were on heightened alert across the nation Monday, but said public threat levels would be raised only if the government learns of credible terrorist threats.

"Our security posture, which always includes a number of measures both seen and unseen, will continue to protect the American people from an evolving threat picture both in the next days and beyond," Homeland Security Secretary Janet Napolitano said.

Ron Smith, chief of the Bureau of U.S. Customs and Border Protection Detroit office, said no specific threat warnings had been issued Monday for the region's border with Canada.

"There has not been an increase in security levels for any of our borders," Smith said. "Obviously, our officers are always vigilant."

Still, Special Agent Donald Dawkins, spokesman for the Detroit office of the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives, urged residents to keep an eye out for suspicious activities.

"Whether firearms violations, explosives violations or any kind of terrorism violation, observation is the key," Dawkins said. "Information from the public is vital."

The money announced on Monday will help Wayne County lead a project to improve communication infrastructure along the border from southeast Michigan to Sault Ste. Marie. The project partners include Detroit; Chippewa, Monroe and Macomb counties, and several Canadian jurisdictions. The award is part of a $25.5-million grant awarded under the Border Interoperability Demonstration Project.