India has pressed social media websites including Facebook and Twitter to remove "inflammatory" content it said helped spread rumours that caused an exodus of migrants from some Indian cities last week.
Reuters reports that the government said it had already blocked access to 245 web pages it said contained doctored videos and images, and the telecommunications secretary, R Chandrashekhar, threatened legal action against the websites if they did not fully comply with the requests to take down the offending pages.
Chandrashekhar told CNN-IBN television that Google and Facebook had largely complied with the government's requests while the response from Twitter had been "extremely poor", though he added that this "may be in part because they don't have an office in India".
Twitter was not immediately available for comment.
Media group Reporters Without Borders said in March that India was increasing pressure on ISPs to supply users' personal data. Google says that between July and December 2011 there was a 49% jump in requests from India for content to be removed from its services, compared with the previous six-month period.
In a move that will likely add to their concerns, the government on Tuesday blocked a number of Twitter accounts that spoof the prime minister, local media reported.
"The government is for free information. There is no question of anything being censored here. But that does not mean there are not limitations," a senior official in the Ministry of Home Affairs said, adding that authorities were trying to identify those responsible for posting the inflammatory material.
Thousands of students and workers from India's northeast fled Mumbai, Bangalore and other cities last week fearing retaliation for violence against Muslims in the remote tea-growing state of Assam after threatening mobile phone text messages and website images sowed panic.
Clashes between indigenous people in Assam and Muslim settlers from neighbouring Bangladesh have killed nearly 80 people and displaced some 300,000 since July.
India has not released details of the blocked pages but said in a statement that "international social networking sites" had indicated that much of the content had been uploaded from neighbouring Pakistan, a long-time foe with which it has fought three wars.
Google and Facebook said they were co-operating with the government.