The rivalry between party veteran V S Achuthanandan and CPI-M Kerala state secretary Pinarayi Vijayan appears to be heading to a flashpoint, pushing the party to its worst crisis in recent times.

Achuthanandan's letter seeking overhaul of the party leadership in the state headed by Vijayan has not only embarrassed the state and central leaders but left the rank and file confused.

Though Vijayan on Sunday night dubbed the "letter bomb" as just another "media creation", Achuthanandan has refrained from denying the reports that he had written such a letter to CPI(M) general secretary Prakash Karat.

The latest turn in the long-running feud between the two leaders has come at a time when CPI(M) is locked in a grim assembly by-election from Neyyattinkara.

The bypoll has been caused by resignation of the assembly seat by R Selvaraj who won in 2011 on a CPI-M ticket. After stunning the party two months ago, Selvaraj is back in the seat as a congress candidate.

To the LDF's discomfiture, the congress-led UDF has been going to town with the CPIM's internal squabbles.

A founder leader of the CPI(M), Achuthanandan has reportedly expressed his reluctance to continue as the opposition leader in the state if the party central leadership refused to intervene in the state affairs.

Achuthanandan, sulking after he failed to get into the politburo in the recently held party congress, was waiting for a chance to strike back at the state leadership.

He has seized on the recent murder of T P Chandrasekharan, leader of revolutionary marxist party, a former CPI-M activist from Onchiyam in Kozhikode district, after which the CPI-M has come under shadow of doubt.

Achuthananandan took strong exception to Vijayan's comment of dubbing marxist rebels like Chandrasekharan as "traitors and renegades."

Last week, Achuthanandan slammed Vijayan, comparing him to S A Dange, late chairman of the undivided CPI before the party split in 1964, openly indicating that Vijayan also might face the plight of Dange, who was later ousted from the party for toeing 'revisionist' line.

The flare-up in the Achuthanandan-Vijayan feud has pushed the central leadership in a bind.

Taking a cautious line in view of the bye-election, both Vijayan and central leaders have reacted to Achuthanandan's move cautiously but signalled that the party would discuss and take decisions at the appropriate time.

"The party is unitedly fighting an election," Vijayan said.

Vijayan said the cadres should be aware of the moves from various quarters to launch an attack on the party. He has also urged all those holding responsible positions in the organisation to maintain restraint till the party discussed the developments and reached a decision.

According to Achuthanandan, rebels who had left the party over various issues, including ideological deviations, should be brought back by convincing them of the correctness of the party line.