"These election results signal a consolidation of the rightwing offensive unleashed after the 2014 election," said an editorial in the CPI-M journal "People's Democracy".
"The reality is that the secular opposition parties, including the Left, were not able to put up an effective challenge to the political and ideological dominance established by the BJP-RSS combine," it said.
"(Prime Minister Narendra) Modi led a campaign which combined belligerent nationalism with a sharply focused communal agenda that sought to rouse majoritarian sentiments in the garb of nationalism.
"The use of unprecedented money power was seen in all spheres of the election campaign. The BJP spent hundreds of crores of rupees in its social media campaign."
The editorial added: "It seems that the BJP's campaign projecting Modi as a strong leader and its communally tinged nationalism making use of the post-Pulwama situation and the Balakot strike have succeeded in overcoming the real problems faced by the people agrarian crisis, unemployment, deteriorating education and health facilities and continuous attacks on minorities, women and dalits."
The CPI-M denounced the Election Commission for failing to ensure a level playing field for the opposition and also for legitimising what it said was "the communal and jingoistic speeches of Narendra Modi and (BJP President) Amit Shah".
It said the CPI-M fought the elections against heavy odds in Tripura and West Bengal and the sweeping defeat of the Left in Kerala was "disappointing and a major setback".
The party will conduct a self-critical examination of this "serious electoral setback", the editorial said.
( With inputs from IANS )