Wawa Welcome America festivities begin under heightened security

PHILADELPHIA (WPVI) -- A week of events to celebrate America's birthday have begun in Philadelphia.

But this year, the U.S. is sounding a holiday terror warning. After a weekend of attacks in other countries, there are new security concerns here for the upcoming 4th of July holiday.

The FBI and Homeland Security have issued a threat bulletin alerting local law enforcement to be extra vigilant over the holidays. But, they say it's not based on any specific threat.

"All the necessary steps are being taken to make every event as safe as it can be," said FBI agent J.J. Klaver.

However, it does come amid rising concern over the danger of "lone wolf" attacks like those we saw on a beach in Tunisia, and at a U.S. owned factory in Paris last week.

The week-long festivities leading up the fourth of July are well underway here in Philadelphia.

That included free admission today at the Franklin Institute.

Ridley Park resident Rich Guerra and his family were among those who say they feel safe enough despite the threat bulletin.

"We're going to have a beautiful day in this beautiful city and enjoy it," said Guerra. "We have plenty of police, fire and EMS here so there's plenty of people to protect us. We're well protected here."

The historic sites on Independence Mall might be inviting targets. But crowds lined up at places like the Liberty Bell pavilion without much concern.

"We're not concerned about that. We know we will be protected and we're really not concerned about the threat from ISIS or anyone else for that matter," said Douglas Jansen from Monroe, Georgia.

There will be big crowds at events all over the city from now through the weekend.

The FBI and police are asking everyone to help protect themselves by keeping an eye out for anything that might look suspicious.

"It doesn't matter if I'm at the ball game or if I'm around here or at a local bar - it wouldn't make a difference. I'm still trying to pay attention to what's going on around me," said Jason Fleming from Sicklerville, New Jersey.

Although there are no specific threats to Philadelphia or anywhere else, Homeland Security is very concerned about the sophisticated efforts to recruit lone wolves on U.S. soil.