Following a warning bulletin from several US agencies about potential terrorist threats around the 4 July weekend, the FBI is establishing command centres to monitor possible terrorist activities.

The bulletin, released on 27 June, stated there was no known active plots, but instead served as a general warning.

According to Fox News, an unnamed federal law enforcement source said authorities were concerned about "soft targets," such as shopping malls or other areas with large crowds and minimal security.

Local, state and federal law enforcement agencies will send information to the command centres, where officials will determine the threat level and respond appropriately, Fox News reported.

The FBI has recently shifted strategy concerning Isis supporters in the US, another law enforcement source told reporters. The agency now hopes to arrest Isis supports on lesser charges before they can go operational. Investigators will then build a broader case when the individuals are in police custody.

On 28 June, Representative Mike McCaul, the chairman of the House Committee on Homeland Security, issued a warning for Americans to "remain vigilant" during the holiday weekend.

"I am extremely concerned about Syrian and Isis recruiters can use the Internet at lightning speeds to recruit followers in the United States with thousands of followers in the United States and then activate them to do whatever they want to do," he said on Fox News Sunday. "Whether it's military installations, law enforcement or possibly a Fourth of July event parade."

Law enforcement officials in the US have stated that Islamist terrorist threat is at the highest level in years, leading to a rise in arrests and charges on homegrown extremist. The bulletin and FBI command centres follow three major Islamist terror attacks in Kuwait, Tunisia and France.