The septuagenarian leader said he has resigned from the primary membership of Congress and a letter to this effect was sent yesterday to party president Sonia Gandhi.

Singh, once a close associate of Gandhi, turned her critic after the Iraqi oil-for-food scam broke out and he was forced to resign from the government in November 2005.

Asked whether he would also quit his seat in the Upper House, Singh, whose Rajya Sabha tenure from his native Rajasthan comes to an end in early April, said "I probably....will leave".

Singh had announced his decision to leave Congress at a BJP rally in Jaipur last week in the presence of Rajasthan Chief Minister Vasundhara Raje.

"You will come to know" was his response when asked about his course of action and whether he would be joining BJP.

"Disqualifying me is not that easy," he said when asked about Congress initiating the process for his disqualification from the Rajya Sabha.