The ministry, in a statement, gave details of the dates of issue and delivery of the letter which Bhattacharjee and Communist Party of India-Marxist (CPI-M) alleged reached the media before it reached the chief minister.
"The home minister's letter to the chief minister, West Bengal was sent by Speed Post on Dec 22, 2010 under No.ED468157705IN. It reached Kolkata GPO on 24.12.2010 at 6 a.m.
The letter should, therefore, have been delivered on 24.12.2010 which was a working day," an official release from the home ministry said.
"Alok Sharma, General Manager, India Post vide his letter dated 27.12.2010 has apologised for the delay in the delivery of the article," it said.
CPI-M had alleged that while the media knew about the letter Dec 24, it reached the West Bengal chief minister Dec 27.
According to sources, the letter dated Dec 21 reached Kolkata GPO Dec 24. However, with Dec 25 and 26 being holidays, it was delivered to the chief minister Dec 27.
The party had also alleged that the purpose of the letter was to serve the interests of the Trinamool Congress, the state's main opposition party.
Chidambaram in his letter had said that complaints received by the central government indicate that armed cadres of the CPI-M were deployed in a covert manner under the guise of 'village protection groups' to guard against Maoist attacks.
"There is evidence to show that the camps are mostly located in CPI-M offices and those of local cadres. It is a matter of grave concern that these cadres have been provided with firearms," he had said.