A letter bomb exploded in a post office on Thursday, trigerring panic in the city few hours ahead of President A P J Abdul Kalam's visit, police said.

No one was injured in the low-intensity explosion, they said.

A sealed envelope, which had some explosive material inside, went off at Manacaud post office on Thursday morning, they said.

Security has been beefed up in the city in view of Kalam's arrival here later in the day.