The Asom Gana Parishad on Sunday bagged the by-poll to the Khumtai assembly seat.
The by-poll was necessitated following the death of Congress legislator Jibakanta Gogoi.
AGP candidate Prabin Gogoi defeated his Congress rival Lachit Phukan by a margin of 3,061 votes, which lifted the total strength of the party to 21 in the house.
"The AGP legislative party leader now has the right to be recognised officially as the opposition leader, as the party has now got one-sixth of the strength of the house as prescribed in the Constitution", assembly secretary M K Sharma said in Guwahati on Sunday.
The latest party-wise strength in the 126-member house is as follows:
Congress-74, AGP-21, BJP-8, Autonomous State Demand Committee-2, Samajwadi Party-1, Samata Party-1 and Independents 19.
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