WASHINGTON (Reuters) - Twitter Inc TWTR.N has shut down more than 125,000 terrorism-related accounts since the middle of 2015, most of them linked to the Islamic State group, the company said in a blog post on Friday.

A 3D printed Twitter logo is seen in this illustration picture made in Zenica, Bosnia and Herzegovina, February 3, 2016. REUTERS/Dado Ruvic

Twitter has said it only takes down accounts when they are reported by other users, but said that it has increased the size of teams monitoring and responding to reports and has decreased its response time "significantly." (bit.ly/1KvrmZ5)

Twitter’s announcement comes as many tech companies – led by Facebook – have taken stronger steps to police controversial content online in the face of threats from legislators to force the companies to report “terrorist activity” on their sites to law enforcement.

Silicon Valley has been wary of engaging with government officials, concerned about endless demands for similar action from countries around the world as well as fears about being perceived by consumers as tools of government.

The announcement was also notable because Twitter has said little about its efforts to combat Islamic State, also known as ISIS, and similar groups even though it has been criticized for not doing enough.

Islamic State, which controls last swathes of Iraq and Syria, has heavily relied on the 300 million-person site, as well as others, to recruit fighters and propagate violent messages.

Seamus Hughes, deputy director of George Washington University’s program on extremism, said Friday’s report showcased an “impressive number” of takedowns, but said that Twitter still appears to police extremist content in a mostly “episodic” way.

Many extremists have migrated toward smaller, less monitored platforms in recent months in response to major Silicon Valley firms stepping up their content policing, Hughes added.

In January, a delegation of top national security officials met tech industry leaders from Twitter, Facebook Inc FB.O, Apple Inc AAPL.O, and Google parent Alphabet Inc GOOGL.O, but most companies, including Twitter, did not send their chief executive officers.

Rep. Adam Schiff, the top Democrat on the House of Representatives Intelligence Committee, called Twitter’s announcement a “very positive development,” but said more was needed.

“Addressing the use of social media by terrorists will require a sustained and cooperative effort between the technology sector, the Intelligence Community, and law enforcement,” he said.

Still, Twitter said in a blog post that it has cooperated with law enforcement when appropriate.

It said that it tries to strike a balance between enforcing its rules on prohibited behaviors, the needs of law enforcement and the desire by users to share their views - including offensive ones.