The court had expressed concern over thousands of illegal migrants being kept in detention centres.

The Supreme Court on Wednesday pulled up the Assam government over inadequacies in the functioning of foreigners tribunals in the state and sought details on it by March 27.

The government told a bench, headed by Chief Justice of India Ranjan Gogoi, that 50,000 migrants were declared foreigners by the tribunal in the past 10 years.

Solicitor General Tushar Mehta, appearing for the Assam government, said around 900 people were kept in six detention centres of the state.

The bench, which also comprised Justices Deepak Gupta and Sanjiv Khanna, said the state government would have to specify through an affidavit whether the foreigners tribunals functioning in the state were adequate and how they were functioning.

The top court, however, added that it was not insisting on the presence of Assam chief secretary in the court at present.

The apex court was hearing a PIL filed by activist Harsh Mander through advocate Prashant Bhushan on the plight of foreigners in detention centres. The plea alleges that they were kept in detention indefinitely just because they were not Indians and were treated as "illegal aliens".

During the previous hearing, the court had expressed concern over thousands of illegal migrants being kept in detention centres for years in Assam without being repatriated or deported to their countries of origin. It had raised several issues connected with the detention centre and said the detainees could not be held for an indefinite period.

The apex court had also sought to know the condition of detention centres, saying the PIL alleged sub-human conditions there.

Mr Mehta had said there was a need for evolving a mechanism for repatriating them and it should be done expeditiously.

The solicitor general was responding to the January 28 queries of the apex court which had asked the Centre and the state to provide details of functional detention centres in Assam and the foreigners detained in them during the last 10 years.

He had told the apex court that 938 people were lodged in six detention centres in Assam and 823 of them have been declared foreigners by tribunals.

The Centre had said over 27,000 foreigners have been pushed back at border points while attempting to enter India illegally.