FBI Director James Comey testifies before the Senate Intelligence Committee on Capitol Hill Wednesday. (Michael Reynolds/EPA)

U.S. authorities have arrested more than 10 people over the past four weeks who were suspected of having ties to the Islamic State, including several who may have been planning terrorist attacks to coincide with the July 4 holiday, FBI Director James B. Comey said Thursday.

The arrests were part of a flurry of law enforcement activity over the past month amid counterterrorism officials’ warnings of a heightened danger of attacks leading up to Independence Day.

During a briefing with reporters at FBI headquarters, Comey said that all of the people arrested were “products” of online recruiting and radicalization efforts by the Islamic State and that “some of them were focused on the Fourth of July.”

Comey did not provide details, but U.S. officials said the list includes previously disclosed cases in New York, New Jersey and Boston.

Comey said that some might not be charged with terrorism-related crimes, an apparent acknowledgment that not all of those arrested had firmly established links to the terror group or were engaged in active plots.

U.S. officials said the arrests reflect a more aggressive stance by the FBI and other law enforcement agencies on how quickly to intervene in cases of suspected online recruitment, particularly after deadly attacks in Tunisia, Kuwait and France last month. Those attacks were determined to have been carried out or inspired by the Islamic State, an al-Qaeda offshoot also known as ISIS or ISIL.

“There is less tolerance for waiting” before making arrests, commented Rep. Adam B. Schiff (D-Calif.), the House Intelligence Committee’s ranking Democrat. “We’ve seen an escalating number of arrests of ISIS-inspired homegrown radicals,” he added. “It’s an extremely worrying trend that we’re going to have to deal with for quite some time.”

Comey, during Senate testimony on Wednesday, said that the Islamic State — which has seized territory in Iraq and Syria and beheaded Western hostages — has called for attacks on members of the U.S. military and law enforcement.

He also said the group has gone beyond its reliance on Twitter and other social media sites and is using encrypted channels to communicate directly with potential recruits.

The Obama administration has used such warnings to put pressure on Silicon Valley companies to design their devices and software in ways that will allow law enforcement to monitor encrypted communications, a proposal many technology companies and lawmakers have opposed.

U.S. officials said the cases cited by Comey include the June 7 arrest of a New York resident, Munther Omar Saleh, 20, who was accused of planning to detonate a pressure-cooker bomb in the city.

Officials said he had described al-Qaeda as “too moderate” in online postings and was seen loitering on the George Washington Bridge.

In another case, Alaa Saadeh, a 23-year-old resident of New Jersey, was charged with providing material support to the terror group and planning with three others to travel overseas to join its ranks.