WASHINGTON » An Islamic State cyber team has threatened two Silicon Valley tech titans, posting a 25-minute video online that shows bullet holes over the faces of Twitter’s Jack Dorsey and Facebook’s Mark Zuckerberg.

Both companies recently stepped up efforts to block postings and accounts that promote violence and Islamic State propaganda after White House officials complained social media companies weren’t doing enough to smother extremist recruiting online.

The potential peril for two social media pioneers is the latest worrying intersection of extremist ideology and the fast-evolving digital technology and online global presence that Twitter and Facebook represent.

Islamic State displays “unprecedented online proficiency,” James R. Clapper, the director of national intelligence, warned the House Intelligence Committee on Thursday at a hearing devoted to national security threats.

President Barack Obama met with his national security team at the State Department on Thursday to focus on the broader threat from Islamic State. Later, he told reporters that the diplomatic push for a cease-fire in Syria’s civil war won’t hamper U.S. airstrikes against the group’s leaders and assets.

“We can hit them anywhere, any time,” he said. The U.S. is “taking them out, day in and day out, one after another after another.”

Though the video probably does not signify an ongoing plot, it could prompt an Islamic State supporter to target employees of the social media giants, according to Rick “Ozzie” Nelson, a former U.S. counterterrorism official now at the nonpartisan Center for Strategic and International Studies in Washington.

“I think it does increase the risk to the employees of those companies, particularly from a homegrown extremist,” Nelson said. “That’s what concerns me the most.”

In addition to organizing or sponsoring deadly terrorist attacks in Europe, Canada, the Middle East and North Africa, Islamic State and its affiliates have used social media to recruit followers and encourage “lone wolf” attacks on the United States and its allies.

The married couple who shot and killed 14 people in San Bernardino, Calif., on Dec. 2 pledged allegiance to the Islamic State leader earlier that morning on Facebook, for example. But they had no known contact with the group.

In May, however, Islamic State claimed direct responsibility for the attempted attack on a Prophet Muhammad cartoon contest in Garland, Texas. Both gunmen were shot dead.

Last fall, FBI bulletins warned that Islamic State was promoting attacks against law enforcement personnel, members of the news media and the U.S. military.

It urged service members to “review their online social media presence for any information that might attract the attention of violent extremists,” including home addresses.

The latest video, purportedly created by pro-Islamic State hackers calling themselves “Sons of the Caliphate Army,” was shared on the messaging app Telegram and was first reported by the online media company Vocativ.

“If you close one account we will take 10 in return and soon your names will be erased after we delete you(r) sites, Allah willing, and will know that we say is true,” reads English-language text in the video.

Twitter announced on Feb. 5 that it had suspended more than 125,000 accounts since mid-2015 for “threatening or promoting terrorist acts,” mostly related to Islamic State.

It’s not clear how effective that effort has been. Islamic State supporters have been known to quickly replace deleted accounts with new Twitter handles.

Twitter declined to comment Thursday, pointing to the Feb. 5 statement that begins, “We condemn the use of Twitter to promote terrorism.”

Facebook, which also declined to comment Thursday, has taken an aggressive approach to identifying and blocking content and users who promote terrorist groups or sympathize with Islamic State.

Speaking Monday at a telecommunications conference in Barcelona, Spain, Zuckerberg said his company is working with governments to prevent terrorist attacks. “We feel a pretty strong responsibility to help make sure that society is safe,” he said.

Apple also has assisted the government in scores of terrorism investigations. But it is fighting a federal magistrate’s order to write software so the FBI can access a locked iPhone used by one of the San Bernardino killers.

Doing so, Apple argued in a motion filed Thursday, would create “a backdoor to defeat the encryption on the iPhone, making its users’ most confidential and personal information vulnerable to hackers, identity thieves, foreign agents, and unwarranted government surveillance.”

The Obama administration has launched a concerted campaign to press social media companies to take bolder steps to prevent extremists from using the Internet to recruit fighters, inspire attacks and publish threats to U.S. officials.

Senior White House officials met with tech executives in San Jose on Jan. 8 to seek their help in thwarting terrorist attacks and preventing online recruitment.

Secretary of State John F. Kerry met with Hollywood studio executives this month to discuss ways filmmakers could counter Islamic State’s online recruitment and exhortations to violence.

On Wednesday, representatives from Facebook, Google, Twitter, Instagram, Snapchat, Tumblr, Microsoft and other companies attended a three-hour meeting at the Justice Department.

The session was billed as the “Madison Valleywood Project” because it brought together Madison Avenue advertising firms, Silicon Valley tech companies and Hollywood film and television studios.

One panel examined Islamic State’s media strategy from a marketing perspective and discussed how to counter the extremist message, according to one attendee who spoke on condition he not be identified.

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Federal agencies have struggled to prevent recruitment over social media, John P. Carlin, assistant attorney general for national security, told the group, attendees said.

The director of the National Counterterrorism Center, Nick Rasmussen, said some social media platforms have taken aggressive steps to take down accounts used by terrorist groups.

Megan Smith, national chief technology officer; Jen Easterly, senior director for counter-terrorism at the White House; and George Selim, head of community outreach for the Department of Homeland Security, also attended.

The Obama administration “is committed to taking every action possible to confront and interdict terrorist activities wherever they may occur, including in cyberspace,” Justice Department spokesman Marc Raimondi said in a statement.

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(Staff writers Christi Parsons in Washington and Paresh Dave in Los Angeles contributed to this report.)

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