By Abhishek Prabhat BBC News, Delhi

The quota plan has led to large-scale protests across India

India's Supreme Court has questioned a federal government plan to increase college quotas for lower castes.

The court was hearing a petition challenging a proposed affirmative action plan that has sparked protests.

But the court also appealed to doctors and medical students, who have been on strike for over two weeks, to call off their protest in the public interest.

Those opposing the affirmative action plan say that the move will lead to lower standards.

Recent developments... infringe fundamental and legal rights of the larger section of citizens Public interest petition

But the move also has the backing of millions of lower caste Indians and other disadvantaged groups.

On Monday, Judges Arijit Pasayat and LS Panta asked the government to explain the rationale of its new affirmative action policy and how it planned to implement it.

Their ruling came in response to a public interest petition filed by a lawyer challenging the plan.

Quota row

Under the new plan, the government intends to reserve nearly half of state-funded professional college places for lower caste students from 2007.

At present, 22.5% of college places are reserved for Dalits, or untouchables, who are at the bottom of India's caste hierarchy, and tribal students.

The new plan would set aside an additional 27% of places in educational institutions for Other Backward Classes (OBCs) - lower caste Hindus and other traditionally disadvantaged groups.

But many Indians fear this would mean fewer places for upper caste students, and lower standards.

"Affirmative action by the government to remove discrimination, inequality and disparity is quite an important step in a healthy democracy," the public interest petition which challenges the government plan said.

"But recent developments in this context, which infringe fundamental and legal rights of the larger section of citizens, create social upheaval, anarchy, chaos and unrest leading to an adverse law and order situation", it added.

The court on Monday also appealed to the protesting doctors to call off their strike in the larger public interest.

Late on Sunday night, the striking doctors and medical students announced plans to further intensify their protests despite a pledge by the government a massive expansion in higher education.