The AICC General Secretary also called the BJP "ungrateful" against the backdrop of a sulking 85-year-old Advani staying away from the executive meet for the first time in his entire political career.
"My heart goes out to Advani ji. He brought BJP from 2 to 182 in Lok Sabha. But then the ungrateful BJP is a Party with differences," tweeted Singh.
"My heartiest congratulations to Modi," Singh said when asked about Modi's appointment.
Taking potshots at the internal difference within BJP, Union Minister and Congress leader Rajiv Shukla wondered when BJP cannot keep its ten leaders together, how will they keep ministers to function together in a government.
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In a dig at Advani, Congress spokesperson Shakeel Ahmed said the BJP veteran was "reaping what he had sown."
"As you sow, so you reap. He had sowed the seeds of communalism in Indian politics. He was replaced by a more communal person," Ahmed claimed.
On micro blogging site Twitter, the Congress spokesperson commented, "Advani hints in his blog that you will have to pay for your sins in your lifetime itself. Is he repenting his role to save Modi in 2002?"