Singh, whose current term in the Upper House ends on June 14, is on a two-day visit here and will file his nomination papers as a Congress candidate in the office of the assembly secretary tomorrow morning for a fourth term to represent the northeastern state of Assam, officials said.

Election to the seat represented by Singh will be held on May 24, when polling for another Rajya Sabha seat held by BJP's Indramoni Bora will also take place.

Notification for the election was issued yesterday. The last date of filing of nominations is May 14 and the papers will be scrutinised the next day.

The last date for withdrawal of candidature is May 17. Counting of votes will take place on May 24.

Singh, an AICC member from Assam and Punjab, became Leader of Opposition in the Rajya Sabha when he was elected for a third term in 2001. Two years later, he became prime minister after Congress President Sonia Gandhi declined the post.

Security arrangements are at a peak in the city in the wake of a bomb attack by the ULFA at Fancy Bazar here on Sunday that injured 19.

One person was killed and 14 were injured a bomb blast during Singh's last visit to Guwahati on April 8.