NEW DELHI (Reuters) - The Delhi High Court ordered the torchbearers of the Nehru-Gandhi political dynasty to appear in court over alleged misuse of party funds, in a new blow for the family that lost power to Prime Minister Narendra Modi last year.

Sonia Gandhi, president of the opposition Congress party, and her son, Rahul, face accusations they used US$13.5 million (S$19 million) of party funds to pay debts accrued by a newspaper business.

Plaintiffs say the transaction benefited a not-for-profit company they own.

The Gandhis deny any wrongdoing.

A spokesman for their Congress party, Abhishek Manu Singhvi, who is also a lawyer representing the Gandhis, said they would challenge the order legally, a move that will likely take the case to the Supreme Court.

Rahul Gandhi is the great-grandson of India's first prime minister, Jawaharlal Nehru. Members of the family have led India for most of its post-independence era since 1947.

Since taking office in 2014, Modi's government has moved to diminish the power of the dynasty, which it accuses of stunting development. The case against the family was brought by Subramanian Swamy, an activist lawyer who is a vocal member of Modi's ruling party.

The mother-son duo will need to appear in a district court in the capital on Tuesday (Dec 8), Swamy told reporters.

A lower court first summoned the Gandhis in June last year. On Monday, the Delhi High Court rejected their plea to exempt them from a personal appearance, another of their lawyers said.

Sonia Gandhi last year accused the Modi-led government of a "political witch hunt" after tax authorities started investigating her party in relation with the same case.