Bangladesh's prime minister visited a stadium Monday where the bodies of three of the 20 victims were taken after a weekend attack in the capital, while security officials questioned some of those who had been rescued as they searched for information on the possible masterminds.

An official involved in the investigation said authorities were still holding five of the 13 people rescued Saturday morning when commandos stormed the restaurant in Dhaka's diplomatic zone, killing six of the attackers and capturing one.

Those detained include a Canadian citizen of Bangladeshi origin, as well as a Bangladesh-born British citizen, he said on condition of anonymity, as he was not authorized to speak to media about the ongoing probe.

He would give no other details of their identities, but said authorities were looking into their backgrounds and questioning their family and friends as well.

The attack — the worst convulsion of violence yet in the recent wave of deadly attacks to hit Bangladesh — has stunned the traditionally moderate Muslim nation and raised global concerns about whether it can cope with the increasingly strident Islamist militants.

That the attackers targeted a popular restaurant in the heart of the diplomatic quarter of Bangladesh's capital signaled a shift in militant tactics. Previously, most attacks were carried out by gangs of young men wielding cleavers and machetes and hacking into their victims before fleeing.

Surrounded by tearful family members and a heavy security detail, Prime Minister Sheikh Hasina along with diplomats from Italy and Japan lay wreaths of white flowers beside the coffins holding the three Bangladeshi victims.

Another 17 hostages, nine Italians, seven Japanese and one Indian, were killed in the attack — many of them tortured with sharp instruments, according to police.

Those bodies were to be flown back to their home countries later Monday. Another two police officers were killed on Friday night when police engaged the attackers in a gun battle.

The stadium vigil was visited by hundreds of Dhaka residents, paying their respects to the victims.

A Catholic Mass, Islamic prayer sessions and a candlelight vigil were being held throughout Monday.

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Associated Press writers Katy Daigle and Nirmala George in New Delhi and Ken Moritsugu in Tokyo contributed to this report.