Washington: Twitter Inc is being sued by the widow of an American killed in Jordan who accuses the social media company of giving a voice to Islamic State, adding to the pressure to crack down on online propaganda linked to terrorism.

Tamara Fields, a Florida woman whose husband, Lloyd, died in the November 9 attack on the police training centre in Amman, said Twitter knowingly let the militant Islamist group use its network to spread propaganda, raise money and attract recruits.

Ambulances leave the King Abdullah bin Al Hussein Training Centre on the outskirts of Amman, Jordan, where a Jordanian policeman opened fire on foreign trainers at a police compound, killing two Americans, one of them Lloyd "Carl" Fields, a South African and a Jordanian. Credit:AP

She said the San Francisco-based company had until recently given Islamic State, also known as ISIS, an "unfettered" ability to maintain official Twitter accounts.

"Without Twitter, the explosive growth of ISIS over the last few years into the most-feared terrorist group in the world would not have been possible," says the complaint filed on Wednesday in the federal court in Oakland, California.