DUBAI, May 17 (Reuters) - Three workers died and several were injured at a building site in Qatar, which has come under pressure to improve conditions for labourers working on venues for the 2022 World Cup, state news agency QNA reported.

Citing the Gulf Arab state's defence ministry, QNA said late on Tuesday that the deaths occurred during an "incident" at a construction site belonging to the Qatari armed forces but gave no details. The ministry "stressed its commitment to abide by the highest safety standards in all its facilities," QNA said.

Qatar, which has long been under fire from rights groups for labour abuses and is under pressure from the United Nations to make changes, has said it is working to improve conditions.

The kingdom denies abusing workers and says it is implementing labour reforms.

In January a British man fell to his death while working at Doha's Khalifa International Stadium -- an incident Qatar's World Cup organizing body said it was investigating. It was the third death on a World Cup site in the last year.

Qatar's efforts to become the competition's first Arab host have been accompanied by accusations from rights groups and labourers that workers were forced to live in squalor and to work without proper access to water and shelter from the sun.

A Bangladeshi man who says he was harshly exploited while working on World Cup facilities in Qatar is suing FIFA for allegedly failing to use its influence to ensure workers are treated fairly.

(Reporting by Sylvia Westall; Editing by Catherine Evans) ((sylvia.westall@thomsonreuters.com; Dubai Newsroom +971 56 216 6204; Reuters Messaging: sylvia.westall.thomsonreuters.com@reuters.net))