PM Cameron said this after launching a £20m language fund to teach English to tens of thousands of Muslim women unable to speak the language. The programme has been launched to build community integration.
According to data available, around 22 percent of around 190,000 Muslim women in England speak little or no English which may make them vulnerable to extremist group like ISIS.
While there was no "causal connection" between poor English and extremism, language lessons would make communities "more resilient", Cameron said, reported the BBC.
UK is home to around 2.7 million Muslims. Immigration rules already force spouses to speak English before they come to Britain to live with their partners.
His comments drew criticism from Muslim groups and opposition parties.
People coming to the UK on a five-year spousal visa will have to face a test after two and a half years to show they are making efforts to improve their English from October.