The veteran leader termed the poll outcome in Tripura, a Communist bastion, "bad" for the CPI(M)-led Left Front, which had been in power in the state for the last 25 years.
The BJP and its state ally, the Indigenous People's Front of Tripura (IPFT), are set to form the next government in Tripura, after securing a majority in the 60-member Assembly in the February 18 election, the results of which were announced today.
"We did not expect this kind of results in Tripura. We were expecting the Left Front to win, at least with a thin majority," Mr Reddy told PTI.
"Ultimately, the BJP manipulated, it is very unfortunate," he alleged.
Asked to elaborate on his allegation of manipulation against the BJP, the CPI leader claimed, "Eleven per cent of the EVMs did not work on the polling day, which created doubts."
Mr Reddy, however, acknowledged that anti-incumbency could have played a role in the north-eastern state after the long period of Left rule.
"It is a blow to the Left Front. We will analyse the reasons for the defeat thoroughly," he added.
Claiming that the BJP spent money "like anything", the CPI leader said, "In a small state, (they) carried out a big campaign. The entire Congress shifted to the BJP. The BJP does not have a base of its own (in Tripura).
"Actually, almost all the BJP candidates are Congress people. The Congress had got more than 30 per cent of the votes earlier (in the previous election)."
Asked about the Left parties steadily losing electoral ground in different parts of the country, Mr Reddy admitted that it was a "big challenge" for the Left.
"But we do think that this is a not going to be a permanent thing. It is a temporary phase (of electoral setbacks to the Left parties). More than politics, manipulation is working (in elections).
"At the same time, the economy is bad, misery and poverty are increasing. So, people are unhappy and angry with the government," he said.