Chaudhry Habib-ur-Rehman, the judge of the Rawalpindi-based anti-terrorism court no. 1, said in an order that all the proceedings and the report of the Pakistani judicial commission that visited Mumbai in March were "illegal."
"The judge ruled that the commission's report is illegal and could not be made part of the records for the case," said Khwaja Haris Ahmed, the counsel for Lashkar-e-Taiba commander Zakiur Rehman Lakhvi, one of the seven accused.
"The court has the right to examine whether the working and report of a commission was duly executed and in this case it ruled that the report was not duly executed. The report will not be read in evidence," Ahmed told PTI.
The lawyers defending the accused had opposed the report of the Pakistani commission, saying it had "no legal value" as the panel was not allowed to cross-examine witnesses during the visit to Mumbai.
The eight-member commission, which included prosecutors and defence lawyers, visited Mumbai and interviewed a judge, a senior police officer and two doctors who conducted the autopsies of the terrorists involved in the attacks and their victims.
Indian officials had said that cross-examination of the witnesses was not allowed in line with an agreement between New Delhi and Islamabad.
Chief prosecutor Chaudhry Zulifqar Ali had earlier told the court that another commission could be sent to India after ensuring that it would be allowed to cross-examine witnesses.
In response to this, Judge Rehman today observed that if India and Pakistan could reach some new agreement that would allow the cross-examination of witnesses, the prosecution could move an application to send another commission to Mumbai.
The judge adjourned the case till Jul 21. Sources said the court's ruling could have an adverse effect on the prosecution of the seven suspects charged with planning, financing and executing the terror attacks in Mumbai that killed 166 people in Nov 2008.
The trial has virtually stalled since last year and the judge has been changed five times since the proceedings began in early 2009.
The sources further said today's court ruling could also affect India's plans to send a judicial commission to Pakistan to probe the Mumbai attacks.
At the conclusion of two-day talks between the Home and Interior Secretaries in May, Pakistan had agreed in principle to receive an Indian judicial commission from India.