The Home Office has issued a statement following the appearance of a video claiming to be of British jihadis fighting for Islamist group Isis.
A spokesperson said the Government "do not tolerate" online extremism and was working to stamp it out.
We do not tolerate the existence of online terrorist and extremist propaganda, which directly influences people who are vulnerable to radicalisation.
"We already work closely with the internet industry to remove terrorist material hosted in the UK or overseas. We also continue to work with charities and community groups to help them challenge those who use the internet to promote extremist ideologies. As part of this, industry specialists have provided training to help them build an effective presence online.
The spokesperson added that the Government was acting to "further restrict access to terrorist material which is hosted overseas" and include extremist material in family-friendly filters.
Leaders of a Cardiff mosque, attended by 3 young men who are now fighting in Syria, say they had nothing to do with their radicalisation.
The Home Secretary has told ITV News that young women have left Britain to fight for the extremists group ISIS in Syria and Iraq.