New Delhi, Sep 5 - State-run power utility NTPC Saturday moved the Supreme Court challenging the Bombay High Court order that had permitted Mukesh Ambani-led Reliance Industries to amend its petition on the ongoing Krishna-Godavari gas row.

In the lawsuit filed in the apex court's registry, NTPC said the July 31 ruling of the Bombay High Court that allows Reliance Industries to amend its response midway through the adjudication process was 'legally untenable'.

The state-run company, which was advised to move the apex court by two of the senior most law officers of the central government, has accordingly sought the revocation of the high court's order.

Reliance Industries had told the Bombay High Court it cannot sell gas to NTPC at $2.34 per unit - which it had proposed in an international competitive bidding - since an empowered group of ministers had fixed the price at $4.2 per unit.

The bid was for 12 million metric standard cubic metres of gas per day for a period of 17 years at $2.34 per unit for NTPC's Kawas and Gandhar expansion projects, both in Gujarat.

But in a separate petition filed before the Supreme Court, the government said the price of $4.2 per unit fixed by the ministerial group was without prejudice to the case being fought by NTPC against Reliance Industries in the Bombay High Court.