Acting on its threat, the Rashtriya Swayamsevak Sangh on Saturdat served legal notice on Union Human Resources Development Minister Arjun Singh demanding an 'unconditional written apology' for his allegation that the organisation was responsible for the assassination of Mahatma Gandhi.

The legal notice, served through fax and speed post by city lawyer Rajesh Gogna on behalf of RSS Delhi state unit, also demanded that Singh give an undertaking that he would not 'misadventure' in future to give any such statement against RSS, organisation spokesman Ram Madhav told PTI.

In the three-page legal notice, the RSS has threatened to file a criminal defamation case against the HRD Minister under Section 500 of the Indian Penal Code if 'he does not comply with the demand for an apology from the RSS', Madhav said.

The notice said that under the legal proceedings the RSS would ask for damages from Singh and all other persons and organisations 'involved in this offence'.

"We also called upon him to explain whether the statement given by him were in his individual capacity or in the capacity of a member of the AICC," the RSS spokesman said.

He said the RSS has also sought to know whether the senior Congress leader gave the statement 'with the consent and on behalf of all the members of AICC'.