From correspondents in Delhi, India, 03:30 AM IST

Airports across India will remain on high security alert till intelligence agencies rule out any threat following an anonymous warning that Al Qaeda was targeting airports in Tamil Nadu and Kerala states, the government said Thursday.

The civil aviation ministry sounded the countrywide alert after the Trichy airport staff found Wednesday an anonymous letter, written in the Tamil language, warning of possible Al Qaeda strikes, Ajay Prasad, secretary in the ministry, said Thursday.

'The letter said that Al Qaeda would be targeting airports in Tamil Nadu and Kerala. We have strengthened the security measures and are not taking any chances,' Prasad told reporters here.

'I cannot categorically say that this letter is a hoax. We cannot take any chances. So we have taken all measures to avoid any untoward incident,' he said.

After the letter was found, the security was tightened at all the airports and measures such as secondary check before boarding, physical checking of hand baggage, increased perimeter guarding and surveillance were put in place, Prasad said.

He said there could be slight delays due to the additional security measures. 'But I think passengers are sensitive enough regarding such issues.'

The Central Industrial Security Force (CISF), which provides security to all civilian airports, had earlier said the specific threat was directed at seven of the airports in the country's south: Trichy, Madurai, Chennai, Coimbatore (all in Tamil Nadu) and Thiruvananthapuram, Kochi and Kozhikode (all in Kerala).

Prasad said the handwritten letter was found in an envelop in a room under construction at the Trichy airport. 'An airport employee found it and handed it over to the airport director as it was addressed to the airport director,' he said.

He said the ministry was in close touch with intelligence agencies and other law enforcing agencies including the state police. A high-level meeting was held with CISF officials during the day to review the airport security.

In Chennai, the purported threat prompted Chief Minister M. Karunanidhi to review security across the state. Police sources said the threat might be linked to the death sentence passed against deposed Iraqi leader Saddam Hussein.

Several cities in Tamil Nadu have seen large protests against the verdict.

Authorities in Tamil Nadu put in place stringent security procedures. Visitors were not allowed into the waiting area. Police dogs were deployed in the airports.

'For the present, the law and order situation is satisfactory. But since I think it can be maintained in a much better manner, I have been frequently meeting senior officers,' the chief minister told the media in Chennai.

In Thiruvananthapuram, Arun Kumar Sinha, the inspector general of police, said airport authorities in Kerala too were on high alert.

'Every passenger arriving or departing from the airports (Thiruvananthapuram, Kochi and Kozhikode) is being frisked,' he said. 'We are leaving nothing to chance. We are also checking vehicles that come and leave the three airports.'

Earlier in New Delhi, a CISF official told IANS: 'As a precaution, vehicles of the airport staff and their baggage are also being checked by the security personnel in letter and spirit.

'Specific instructions have been issued to officials posted at different airports to ensure the passengers are not harassed and there should not be any panic.'

The CISF has also posted 'spotters' - men trained to identify suspicious people - at the airports.

(Staff Writer, © IANS)