The BJP wrested Tripura, the last Left bastion, and received invitation to be part of the government in Nagaland, while Meghalaya elected a hung Assembly.
Elections were held in 59 seats in all three states due to different reasons despite them having 60-member assemblies.
Uttar Pradesh Chief Minister Yogi Adityanath, who had campaigned in Tripura, said, "The party is achieving historical success in Tripura, Nagaland and Meghalaya under the able leadership of Prime Minister Narendra Modi and I want to congratulate all party workers, PM Modi and party president Amit Shah."
State BJP chief Mahendra Nath Pandey also attributed the party's performance to the prime minister and Shah.
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"BJP has breached the bastion of the communists in Tripura, and has also registered a win in Nagaland along with its allies," he said.
In Uttarakhand, Chief Minister Trivendra Singh Rawat said the BJP's poll victory in Tripura was the triumph of Modi's agenda of development and the party president's efficient leadership.
"By turning the policy of'look east' into that of 'act east', the prime minister has given a new direction to the development in eastern India. The poll verdicts show that people in thenortheast have embraced the PM's policies," Rawat said in a statement.
"With its impressive performance in the northeastern states of Tripura and Nagaland, Modi and his party have got the fresh political and electoral legitimacy to take on the challenges confronting the country and the region on economic and political fronts," state works minister Naeem Akhtar said.
He is also the state government's spokesman.
The minister also reiterated that the resolution of momentous problems confronting Jammu and Kashmir should be brought to the centre-stage with fresh political resolve.