India's Prime Minister Manmohan Singh smiles before a meeting in New Delhi in this December 5, 2008 file photo. [Photo/Agencies]

NEW DELHI - A special Indian court on Wednesday made the country's former Prime Minister Manmohan Singh an accused in the multi-billion dollar coal scam and summoned him in a major embarrassment for the main opposition Congress party.

The court asked the former prime minister and five others to appear before it on April 8 after charging Singh with criminal conspiracy, corruption and breach of trust, brushing aside suggestions by India's premier probe agency that it did not have any prosecutable evidence against him.

This particular case relates to the misselling of a coal field in the eastern state of Odisha in 2005 to Hindalco, owned by billionaire industrialist Kumar Mangalam Birla, when Singh also held the charge of the Coal Ministry.

Singh, who was the country's prime minister from 2004 to 2014, had been earlier questioned by the Central Bureau of Investigation last year, which is probing the case under the orders of the country's Supreme Court. He has denied any involvement in the alleged scam.

In fact, this is one of the several cases in the coal scam, dubbed as coalgate, in which the then Congress-led United Progressive Alliance government allegedly sold coal fields to private companies at prices below the market rate without auction, causing billions of dollars loss to the state exchequer.

The coal scam was unearthed by the state auditor in 2012. And in 2014, the country's Supreme Court had scrapped nearly 214 coal blocks allocated by successive governments over the past two decades.

The development has evoked reactions from various political parties, with the ruling Bharatiya Janata Party (BJP) blaming the Congress party for putting the former prime minister, who is otherwise said to have a clean image, in a spot.

The Congress has, however, rejected the charges. "It needs to be understood that the Supreme Court did not pass even a whisper of a stricture on former Prime Minister Manmohan Singh. He and the former government conducted itself with utmost transparency," party spokesperson Manish Tewari said.