By Masud Karim

By Masud Karim

DHAKA, Aug 27 (Reuters) - Bangladesh has not ruled out foreign involvement in a grenade attack on an opposition rally last week that killed 19 people and wounded more than 150.

The government, faced with domestic and international pressure after the attack on the rally addressed by former prime minister Sheikh Hasina, sought Interpol's help on Thursday in investigating the violence.

"In fact, we are weighing all the domestic and foreign aspects of the blasts," Reaz Rahman, adviser to the Foreign Ministry, told Reuters when asked if the government suspected a foreign hand.

"We will rely on Interpol as it is the most credible (organisation) with a huge anti-crime network across the world.

"We need Interpol's assistance to probe the grenade attack as we do not have adequate expertise to handle such a big crime," Rahman said. He did not elaborate.

At least seven grenades exploded at Hasina's rally and the main opposition Awami League leader said the attack was an attempt to kill her.

Bangladesh, a volatile Muslim-majority democracy, has been rocked by a series of mysterious bombings since 2000 which have killed more than 105 and wounded more than 500.

The bombers have set off explosions at cinemas, concerts, opposition rallies and minority religious institutions.

Prime Minister Khaleda Zia's government has been unable to catch the bombers and is facing criticism for its inability to stop them. The British High Commissioner was wounded in a blast in May in Sylhet town in the northeast.

The government accepted Scotland Yard's help in investigating the Sylhet blast, but this is the first time it has asked Interpol for aid. Government officials were not available for comment on whether Interpol had replied to the request.

The Awami League and Hasina, whose hearing in both ears has been temporarily impaired by Saturday's blasts, say militants close to Islamic parties in Khaleda's ruling coalition were behind the attack.

Khaleda's Bangladesh Nationalist Party has rejected the allegations, condemned the blasts and vowed to hunt down the culprits.

Hasina received a death threat on Tuesday from a previously unknown Islamic group which said it would target her within seven days. Police said they were investigating.

PROTESTS

Saturday's attack has led to opposition protests and strikes. More than 230 people have been injured and one person killed in attacks by opposition supporters on trains, railway stations, vehicles and government offices and in clashes with police.

On Friday, a holiday in Bangladesh, about 200 Awami League supporters formed a human chain in front of Supreme Court in Dhaka and put up a black banner which read: "We want an international probe into the heinous carnage".

The Awami League has called for another general strike on Saturday.

Analysts say the government has to act to stop the security situation from deteriorating and the U.S.-based Human Rights Watch called on the government to catch the bombers.

"The ... government must make, and be seen to be making, every step to apprehend the perpetrators of these attacks," Brad Adams, a senior official of the group said in a statement from New York.

Separately, the government saw off another challenge to its authority when a plan by an alliance of radical Muslims to lay siege to a minority sect's mosque fizzled out following the arrest of two alliance leaders, deployment of a strong police force and monsoon rains.

The radical alliance says the Ahmadiyya Muslim sect sees its leader as the last prophet, which mainstream Muslims, who believe the last prophet was Muhammad, would call heretical.

Ahmadiyyas deny considering their leader the last prophet but nevertheless, the radicals want the sect declared non-Muslim.

Hundreds of riot police equipped with shields, teargas and rubber bullets, took up position in heavy rain around the Ahmadiyya mosque in Dhaka while about 600 sect members went to say Friday prayers. No radical protesters turned up. (Additional reporting by Anis Ahmed and Nizam Ahmed)