Police officials requesting anonymity said a primary investigation suggested local militant links to the bomb blast that injured the Bangladesh-born envoy and killed three shortly after Friday prayers at the shrine mosque.

Harkatul Jihad, Hizb ut-Tahrir, Hizbut Towhid and Shahaba Sainik Parishad with a militant past are among the seven organisations, but a senior police official, talking to The Daily Star, would not name the three others before the probe closes.

Investigators are also chasing links between the local operatives and international militants that took a hard line on the US or UK in the wake of Iraq war.

Hizb ut-Tahrir allegedly posted anti-British and -US posters around the shrine two days before the bomb blast, second in five months at the 700-year-old heritage site.

An alleged Harkatul Jihad member, Shamim, was taken into police custody and released after interrogation last night.

Another source said help from UK intelligence agencies is crucial to finding leads to the attack as close ties may exist between Islamic groups in London and local religion-based organisations.

But Sylhet Deputy Inspector General of Police Ali Imam Chowdhury and Superintendent of Police Shahadat Hossain said no investigated findings can be revealed as the probe is going on.

"All possible ways are being considered for investigation," said the SP hours before he was suspended for failing to provide adequate security during the British envoy's visit.

WATCH ON MADRASAS

Intelligence agents are keeping a close watch on some madrasas blamed for spreading militant messages and a Rapid Action Battalion (RAB) team from Dhaka has inspected several madrasas since Sunday with more in a few days, the police official said.

The religion-based parties and Islamic militants spread their network to the madrasas, making the Islamic schools first steps to broader politics along religious lines.

GRENADE SOURCE

Some police officials said the investigators would also probe cross-border gunrunning as the grenade thrown at the high commissioner was not locally made.

Individuals or groups trained in charging grenades are now under sharp watch.

ANTI-SHRINE SUSPECTS

A series of incidents at Hazrat Shahjalal Shrine, including poisoning of fish and a fatal bomb blast on January 12, has triggered a frenzy of speculation.

As the incidents at the shrine came after anti-shrine comments by Jamaat-e-Islami leader Delwar Hossain Saidee, agencies are also considering any anti-shrine group's involvement.

WHO THREW THE BOMB?

Police suspect three men, part of hundreds of wanderers who live at the shrine, as they were right above the shrine gate and close to the blast scene. Asked about their suspected roles, shrine authorities told police that they were "only cleaning."

Police last night raided the house of Jewel, who rushed off by motorbike right after the blast and are trying to track down a suspect known as Mama.