Official sources said Prime Minister Atal Behari Vajpayee, who took a serious view of the incident, directed Singh to order the probe and submit a report at the earliest.

Vajpayee had earlier directed Delhi Police Commissioner V N Singh to look into the issue and fix responsibility, the sources said.

They said the reported verification of Sareen's character and antecedents was not at the behest of the Prime Minister's Office but apparently a part of ``routine security exercises.''

Such an exercise is undertaken on participants in the week-long annual conference, but it was a ``goof up'' on the part of the police to have stretched it to include even the Air Force chief, they said.

The conference is scheduled to be addressed by Vajpayee.

It was ``even more silly'' tohave sent a junior officer from the Uttar Pradesh police to Sareen's residence at Dehradun for reported verification, they said.

The sources said the chiefs of armed forces frequently met VVIPs, including the prime minister, and by no stretch of the imagination could they be covered by ``routine security drills.''

On Congress leader Rajesh Pilot's demand that the PM order a high-level enquiry into the incident, they said such security checks had begun in 1995 when Pilot was Minister of State for Internal Security.