Many of the sites are dedicated to recruiting young people to fight for Islamic State in Syria and Iraq.
And the amount of online material encouraging jihad is constantly growing, detectives said.
The Counter Terrorism Internet Referral Unit – a police squad which fights online extremism – has removed 140,000 items of propaganda in the past five years.
Security minister John Hayes said: “We have seen an increase in the scale and pace of terrorist communications by groups like Isis, encouraging vulnerable young people to travel to conflict zones like Syria and Iraq.
Mr Hayes urged internet service providers and social media companies to remove terror-related material.
Content already targeted for removal includes a video, viewed more than 5,000 times on YouTube, which describes non-Muslims as “not worth anything, less than an ant, less than an insect, less than a dog”.
She proposed civil orders similar to Asbos designed to restrict internet use by fanatics and to stop them speaking at public events.
Breaching the orders, which have not yet been introduced, would be a criminal offence.