President Barack Obama has called on Silicon Valley to help address the threat of militant groups using social media and electronic communications to plan and promote violence, setting up renewed debate over personal privacy online.
"I will urge high-tech and law enforcement leaders to make it harder for terrorists to use technology to escape from justice," Obama said in a televised Oval Office speech on Sunday.
Obama used the address to try to reassure Americans nervous about possible future attacks after the shooting deaths of 14 people at an office party in San Bernardino, California, by a husband and wife with radical Islamist views.
The shootings have reinvigorated a long-running debate about Washington's digital surveillance effort to find and capture violent extremists, with the recent shutdown of a US mobile phone spying program coming under renewed criticism.
The White House wants tech firms to help by restricting the use of social media for violent ends, a senior administration official said on Sunday, speaking on background.
In coming days, the White House will talk to companies in the tech sector about developing a "clearer understanding of when we believe social media is being used actively and operationally to promote terrorism", said the official.
Obama sees the need for the sector to work with law enforcement when the use of social media "crosses the line" from expressing views "into active terrorist plotting", the official said.
"That is a deeply concerning line that we believe has to be addressed. There are cases where we believe that individuals should not have access to social media for that purpose," the official said.
There have also been calls to weaken encryption to make it easier for the government to monitor communications. This idea has met fierce opposition from technology companies and privacy advocates, who warn that weaker encryption would expose data to malicious hackers and undermine the internet's integrity.
The White House wants to continue to talk to Silicon Valley about encryption, saying US allies in Europe and elsewhere "want to make sure that encryption is not utilised in a way that allows for a space, a dark space, for terrorist groups to be plotting operations and attacks", the official said.
Some legislators were expected to revive controversial legislation that would require social media sites such as Facebook and Twitter to inform the government about posts that are deemed to promote "terrorist activity".
The debate has also become part of the 2016 presidential election campaign. On Sunday, Hillary Clinton, the front runner in the Democratic race, said tech firms need to stop groups from recruiting and directing attacks, and from celebrating violence.
Twitter declined to comment on Clinton's comments, and Facebook and Google did not immediately respond to requests for comment.
Current and former federal officials, internet company executives and outside experts all told Reuters that since IS attacks in Paris in November, Facebook, Twitter and YouTube have taken down more propaganda than ever before in the past year - on their own and in tandem with officials and activist groups.
