Mr. Ben Jeddou, a former judge and an independent politician, said he felt the Tunisian smugglers were connected to Al Qaeda in the Islamic Maghreb, a Qaeda affiliate that was recently involved in establishing guerrilla training camps and laying mines in a mountainous area near the border with Algeria.

Some suspects detained in Mr. Belaid’s assassination in February were members of Ansar al-Sharia, a Salafist group in Tunisia also known to have links with Al Qaeda. The group was also behind an attack on the United States Embassy in Tunis in September, and its leader, Abu Ayad, had trained and fought with Qaeda operatives in Afghanistan.

American telephone intercepts have shown that Abu Ayad was in contact with Al Qaeda at the time of the embassy assault in Tunis, Tunisian officials have said.

The government’s revelations about the suspects may assuage some anger among opposition groups who have accused the government, and specifically Ennahda, the moderate Islamist party that leads the governing coalition, of being too lenient in its treatment of Islamists and allowing the killings to occur.

Ennahda has condemned the killings and accused those behind them of trying to derail the transition to democracy.

Opposition demonstrators gathered sporadically on Friday on the main Habib Bourguiba thoroughfare here, shouting slogans but flagging rapidly in the blistering heat. Protesters have also begun to camp out in front of the National Constituent Assembly building.