Two American students' desire to keep a small relic of famous Taj Mahal [Images] landed them into trouble when they were detained for interrogation for almost three hours by ASI and CISF officials said.

The students identified as Stephen and William had picked up a black stone while visiting the area under renovation at Taj Mahal. It is not clear whether the stone had fallen from the building or the students took it out.

A group of nine American students came to visit Taj Mahal. The incident took place when one of the students picked up a black stone from the site of restoration work, said Raghuveer Lal, SSP Agra [Images] said.

The ASI official, who saw the incident, immediately alerted the CISF, who frisked the students and recovered the stone. Two students, Stephen and William, were detained for interrogation.The students have apologised for the incident, said the SSP adding that the ASI is investigating and a complaint will be lodged with American Embassy if the students are found guilty.