Republican U.S. Sen. Ted Cruz on Tuesday accused the Obama administration of under-emphasizing the "threat of radical Islam" as he presided over a Senate hearing for the second time since suspending his presidential campaign in early May.

President Barack Obama and top Justice Department officials have come under fire from conservatives for avoiding the term "radical Islam" when denouncing attacks by violent extremists who claim inspiration from Islamic State, such as the Orlando, Florida, nightclub shooter.

Administration officials have countered that focusing on the use of the phrase is a political distraction and gives fuel to Islamic State propagandists who say the United States has waged war against all of Islam.

Absent from Tuesday's hearing before a subcommittee of the Senate Judiciary Committee were the two top Justice Department counter-terrorism officials whom Cruz had invited to testify.

"The Obama administration of course has declined to appear and explain its policies," Cruz said at the hearing, noting that the officials had not provided any reason for staying away.

Justice Department spokesman Marc Raimondi said in an emailed statement that the department is "focused on aggressively and successfully pursuing terrorist adversaries" and on denying them "unchallenged recruiting platforms to spread their messages of hate and intolerance."

Democratic members of the subcommittee said national security policies more targeted at Muslims, such as presumptive Republican presidential nominee Donald Trump's call for a ban on Muslim immigrants, would be unconstitutional and counter-productive.

"We cannot fight radicalization with further radicalization," said Democratic Senator Christopher Coons of Delaware, adding at the end of the hearing that he did not think "arguing over semantics" for three hours had helped improve American national security.

Experts from Muslim and Arab advocacy groups as well as former government national security officials testified at the hearing, representing both sides of the debate over whether the administration emphasizes Islam too much or too little in its counter-extremism policies.

Protesters with Code Pink, an anti-war advocacy group, offered Cruz packs of gum labeled "Islamophobin" as he entered the hearing room, telling him it could cure Islamophobia.