The US Secret Service launched an urgent investigation into its own security procedures after a couple gatecrashed a glittering White House state dinner for the Indian prime minister and posted the pictures on Facebook.

Michaele and Tareq Salahi were not on the guest list for Tuesday's dinner, agency spokesman Ed Donovan said.

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President Barack Obama was never in any danger because the party crashers went through the same security screening for weapons as the 300-plus people actually invited to the dinner honouring Indian premier Manmohan Singh, Mr Donovan said.

The Washington Post, which first reported on the Salahis' evening out, said the couple were well-known in the Virginia horse-country set.

The Secret Service learned about the security breach yesterday after a media inquiry prompted by the Salahis' online boasts about having attended the private event, Mr Donovan said.

One of the many photos from the dinner posted on Michaele Salahi's Facebook page shows the couple with a smiling US vice president Joe Biden.

In other photos, they appear alone or together with White House chief of staff Rahm Emanuel, Washington Mayor Adrian Fenty, CBS News anchor Katie Couric, Republican Rep Ed Royce and three US Marines in their dress blues.

Mr Donovan would not comment on whether the couple had been contacted by the Secret Service, how long they were on the White House grounds or other details of the investigation.

The Post said uninvited guests who got in could face a potential trespassing charge unless someone from inside the White House staff slipped them in.

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The agency's Office of Professional Responsibility was reviewing what occurred. An initial finding indicated that a checkpoint did not follow proper procedures to ensure the two were on the guest list, Mr Donovan said.

"It's important to note that they went through all the security screenings - the magnetometer screening - just like all the other guests did," he said.

He added that Mr Obama and others under Secret Service protection had their usual bodyguards with them at the dinner.