"We respect the verdict of the people of West Bengal," party general secretary Sitaram Yechury told the media.
"We will examine the reasons and review these results as far as the Left Front's poor performance is concerned and the tactics we adopted there," he said.
Despite opposition from a section within, the Communist Party of India-Marxist allied with the Congress to take on the Trinamool Congress. In the end, the Left got fewer seats than even the Congress.
The CPI-M leader also accused the Trinamool of unleashing "terror and intimidation" on his party cadres even during the election process.
"Four of our comrades were killed during the campaign. Even today, at the counting centres, there were clashes."
He said the entry of the BJP in the West Bengal assembly had been marked by an "understanding" between the former and the Trinamool.
In Tamil Nadu, Yechury admitted that the Left and its allies got squeezed out because of the "bipolar state in Tamil Nadu".