Mr. Molins said that investigators had not uncovered a specific target or date for the planned attack and were trying to identify other accomplices. Under questioning, he said, Mr. Kriket denied being a terrorist, said he had rented the Argenteuil apartment on behalf of someone whom he would not name, and said the unidentified man and an accomplice were the bomb makers.

Three men have been held in other countries on suspicion of working with Mr. Kriket. One is Mr. Bahri, whom the Dutch police arrested in the port city of Rotterdam on Sunday at the request of the French authorities. The other two are Algerians who were arrested in Brussels on Friday: Abderahmane Ameroud, 38, and a man identified only as Rabah M., 34. (He was previously identified as Rabah N. and Salah A.)

Mr. Ameroud had been convicted of providing logistical support to two Tunisian suicide bombers who assassinated Ahmed Shah Massoud, an Afghan opposition leader, two days before the Sept. 11, 2001, attacks in the United States. In 2005, Mr. Ameroud was found guilty of complicity in the murder.

Mr. Ameroud was also linked to an Afghan and Pakistani network suspected of training would-be jihadists in a forest near Paris and in the French Alps. He was convicted of participation in a terrorist enterprise in 2007 and was thought to have been deported to Algeria after serving his sentence.

On Wednesday, a court in Brussels delayed proceedings against him and Rabah M. to April 7, at the request of their lawyers.

Also on Wednesday, a government official said that a file with the floor plan and photographs of the office of the Belgian prime minister had been found on a laptop computer discarded in a garbage can last week by one of the terrorists linked to the Brussels attacks. It was found during a raid in the Schaerbeek neighborhood hours after the attacks.

Several Belgian newspapers, including L’Echo, De Tijd and De Morgen, reported that the information about the prime minister’s office, the site of regular meetings of cabinet ministers, had been found on the laptop.