Read the threat assessment The director of national intelligence released his assessment of threats to the United States, which covers cybersecurity, nuclear weapons, threats related to economic trends and natural resources, and more. Read it.

The nation’s spy chief called on former intelligence contractor Edward Snowden to return a massive trove of classified documents on Wednesday during a congressional hearing on security threats that was dominated by heated exchanges over that security breach and the surveillance programs subsequently exposed.

Speaking before a Senate panel, James R. Clapper Jr. outlined an array of dangers to American interests, including a rise in cyberthreats and the emergence of Syria as a magnet for Islamist militants linked to al-Qaeda.

But after skimming through those developments, Clapper focused his opening remarks on Snowden, delivering a blistering stream of criticism in which he described the former contractor for the National Security Agency as a hypocrite who has severely undermined U.S. security.

Clapper said the documents exposed by Snowden have bolstered adversaries, caused allies to curtail cooperation with the United States, enabled terrorist groups to alter the ways they communicate, and put lives of U.S. intelligence operatives at risk.

“Snowden claims that he has won and that his mission is accomplished,” Clapper said. “If that is so, I call on him and his accomplices to facilitate the return of the remaining stolen documents that have not yet been exposed to prevent even more damage to U.S. security.”

Clapper did not clarify what he meant by “accomplices,” or whether he was referring to journalists who have received documents from Snowden. A spokesman said Clapper was “referring to anyone who is assisting Edward Snowden to further threaten our national security through the unauthorized disclosure of stolen documents related to lawful foreign intelligence collection programs.”

There were a number of sharply worded exchanges during the annual worldwide threat hearing — an ordinarily sober discussion — turning it into a platform for U.S. intelligence officials and some of their critics in Congress to vent months of pent-up frustration with the Snowden fall-out.

[Read a full transcript of Wednesday’s hearing]

At one point, Sen. Ron Wyden (D-Ore.) decried what he described as a “culture of misinformation” among U.S. intelligence officials, cataloguing misstatements and falsehoods that had been exposed by Snowden.

Trust in those agencies “has been seriously undermined by senior officials’ reckless reliance on secret interpretations of the law and battered by years of misleading and deceptive statements,” Wyden said.

Among the most pointed examples was Clapper’s testimony before the same committee last year that U.S. spy agencies did not gather data on millions of Americans. Months later, Snowden’s disclosures showed that the NSA had secretly compiled a database containing the phone records of nearly every American.

The recriminations over Snowden come as President Obama has pledged to end the NSA’s collection of such records and underscored the extent to which Snowden-related damage control has been a major distraction for spy agencies struggling to keep up with rapidly shifting security threats.

U.S. officials on Wednesday warned that political turmoil in the Middle East was accelerating the atomization of the al-Qaeda terrorist network, with offshoots gaining strength in Syria, Yemen, Iraq and Egypt.

Clapper said that Syria has attracted about 7,000 fighters from as many as 50 nations beyond its borders, including a steady flow from the Middle East and Europe. The trend has alarmed counterterrorism officials, raising concern that militants trained and indoctrinated in Syria might use their Western passports to carry out attacks against the United States or its allies.

Syria is “in some respects a new FATA,” Clapper said, referring to the tribal belt of Pakistan where al-Qaeda has been based for more than a decade. One of the leading militant groups in Syria, known as Jabhat al-Nusra, “does have aspirations for attacks on the homeland.”

His concern was echoed by senior lawmakers, including Sen. Dianne Feinstein (D-Calif.), the chairman of the Senate Intelligence Committee, who noted that the friction among Islamist groups in Syria has become “so dire that even al-Qaeda’s central leader . . . has denounced the activities of one group as too extreme to countenance.”

A spike in violence in Iraq has brought the number of attacks there to levels not seen since U.S. forces left in 2011, U.S. officials said.

They also warned of a spike in threat reporting associated with the upcoming Olympic Games in Sochi, Russia. Citing extensive security at the Olympic venues, Matthew Olsen, director of the National Counterterrorism Center, said, “The greater threat is to softer targets in the greater Sochi area, and in the outskirts.”

On Iran, Clapper warned that a move by Congress to impose new sanctions could unravel a deal reached last year to ease economic penalties on Tehran in return for shutting down key parts of its nuclear program. North Korea, meanwhile, has expanded its uranium enrichment facility, he said, and restarted a plutonium reactor, following through on recent threats to resume nuclear weapons work.

U.S. officials repeatedly refused to answer questions about U.S. surveillance programs, citing their classified nature. Still, the hearing produced new hints about secret capabilities not exposed by Snowden.

Sen. Mark Udall (D-Colo.) noted that the CIA is banned from domestic spying and searches of Americans inside the United States but asked CIA Director John Brennan if he could assure the committee that it does not engage in such operations.

“I can assure the committee that the CIA follows the letter and the spirit of the law in terms of what CIA’s authorities are,” Brennan said in a carefully worded reply.

Wyden, who works closely with Udall on intelligence matters, asked Brennan whether the CIA abides by a separate anti-hacking statute that makes it a crime to break into a network without authorization. “I would have to look into what that act actually calls for and its applicability to CIA’s authorities,” Brennan said.

Though far smaller than the NSA, the CIA’s Information Operations Center has for more than a decade carried out operations to penetrate adversaries’ networks, but it is supposed to do so only overseas.

Separately, FBI Director James Comey acknowledged for the first time publicly that the bureau does not need a warrant to obtain Americans’ cellular site location information from carriers in intelligence investigations.

Instead, it relies on a lower standard that agents have reason to believe the data sought would be “relevant” to an authorized investigation. That may not be true for all types of location data, however. The Justice Department has stated that its policy in criminal probes is to require a warrant for the more precise GPS data, when investigators want it prospectively, in real time.

U.S. officials defended the NSA’s collection of Americans’ phone records, which a federal judge and separate White House advisory panels have said violates the Constitution and has been of little use in detecting terrorist plots.

Comey said he understood privacy concerns about the program but said it helps the bureau assess whether there is a broader terrorist cell or network in the United States in the aftermath of an attack such as the Boston Marathon bombing. “It allows us to do in minutes what would otherwise take us . . . hours,” Comey said.

Ellen Nakashima contributed to this report.