[WASHINGTON] Airlines flying to Winter Olympics host Russia are being warned to watch for toothpaste tubes containing materials that could be used by terrorists to make a bomb, according to a US law enforcement official.

The official declined to elaborate on the intelligence that sparked the alert, which was sent on Wednesday to US and foreign carriers, just two days before the start of the 2014 Games in Sochi, Russia. The official wasn't authorised to discuss the warning publicly and asked for anonymity.

Security at Sochi is tight in response to threats of terror strikes by Islamic militants. The Black Sea resort is just a few hundred kilometres from the North Caucasus region, where Russia has been battling Islamic extremists.