An American citizen held at IGI airport here with a knife remained in detention for the third day on Friday as the security agencies were corroborating his statement besides awaiting a clearance from the FBI.

The 61-year-old Winston Marshall Carmichael, who was detained in the wee hours of February10 when he was to board a Qatar Airways flight to Doha, had been subjected to extensive questioning by several agencies.

The US Mission in New Delhi was informed about the arrest after which a team of FBI officials visited and took details from Carmichael, a resident of New York, official sources said.

The US national, who was being quizzed to probe if he was a similar operative like Lashker-e-Toiba suspect David Headley, was detained at the Indira Gandhi International Airport after a 4.3 by 1.5 inches knife concealed in a herbal plant 'Shilajit' was recovered by CISF from his hand baggage.

The knife, though, was too small to be considered in the category of a weapon.

A chemical examination of the herbal plant was also being conducted, the sources said.

However, the security agencies were also awaiting a clearance from the FBI who were verifying his activities back in the US, the sources said.

Carmichael, a convert from Christianity to Islam, had a tourist visa to India, Pakistan and Bangladesh and came here from Bangladesh.