A Jerusalem-based lawyer has claimed that Twitter is providing services to foreign terrorist organizations such as "Hizbollah and other foreign terrorist organisations".

Nitsana Darshan-Leitner, who specialises in cases against terror groups, criticised the social networking site for allowing such organisations to use the site and said that the company could be violating US law.

In a letter to the company's CEO, Richard Costolo, she suggested that allowing terrorist groups to use the site constituted "the type of seemingly innocuous material support that would render [Twitter] personally criminally and civilly liable".

Although Hizbollah does not have an official Twitter account, the al-Manar television network, which it controls, has 7,500 followers. Groups such as Hamas also use the site either through officials or proxy accounts.

Ms Darshan-Leitner is one of the founders of the Shurat HaDin law firm. Last year Shurat HaDin lawyers claimed a key part in stopping the second Gaza flotilla last year by warning the boat insurers that they could be charged with "aiding terrorism".

Twitter is not the only form of social media to face criticism for not challenging racist or antisemitic activity online. There have been numerous calls for Facebook to clamp down on this, including by Shurat HaDin.

The issue was also raised in the US Congress last week by former vice-presidential candidate Joe Lieberman. Senator Lieberman, who chairs the Senate Homeland Security Committee, called for Twitter to block the accounts of feeds that glorified Taliban attacks on NATO troops in Afghanistan.