India's ex-Prime Minister Singh and five others facing accusations in a coal-mining scandal have been summoned by an investigative court. In 2012, auditors accused officials of under-pricing coalfields during auctions.
Investigative judge Bharat Parashar on Wednesday told Singh to appear before him on April 8 to answer a series of corruption-related charges, including criminal conspiracy and breach of trust, according to Indian media.
Singh, whose Congress party conservatives lost office in last year's federal election, was in charge of India's coal ministry during his term as prime minister from 2004.
Singh was questioned in January by India's Central Bureau of Investigation (CBI) and has previously denied any wrongdoing on his part.
Last year, India's Supreme Court scrapped all 218 allocations of coal reserves made between 1993 and 2010, saying procedures lacked transparency. Many of the allocations had been awarded during Singh's government term.
Industrialist also summoned
A former coal ministry secretary and the multi-billionaire Kumar Mangalam Birla, who heads the Hindalco Industries, have also been summoned.
India's expanding economy relies of coal for two-thirds of its electric power generation.
Current Prime Minister Narendra Modi and his nationalist Bharatiya Janata Party won last year's election on the back of the scandal.
Modi's government has launched a process to re-auction the coal blocks.
Singh and the other defendants, if convicted, could be sentenced to jail terms of up to life imprisonment.
(ipj/sms AP, dpa, AFP)