Dhaka - A court Tuesday sentenced three Islamist militants to death for an attack on a former British high commissioner to Bangladesh four years ago, officials said.

The court sentenced two other militants to life imprisonment for the 2004 grenade attack on Anwar Choudhury, the former British envoy to Bangladesh, in the north-eastern shrine city of Sylhet.

Three policemen were killed and more than 50 people were injured, including Choudhury, in the attack at the shrine of Shah Jalal, a 13th-century Muslim saint.

The operation commander of Harkatul-Jihad-al-Islami (HuJI), Mufti Abdul Hannan, told the court immediately after the verdict was handed down that the order was unjust.

"We will prove ourselves innocent in the higher court," a court official quoted him as saying.

The Criminal Investigation Department found involvement of the HuJI, an outlawed organization, in the attack.

Choudhury, a Bangladeshi-born British diplomat, was attacked on May 21, 2004, just five days after becoming British high commissioner to Dhaka.

The country was rocked by a series of attacks mainly by the Islamist insurgents between 2004-06. Bangladesh authorities executed six ranking militants of Jamaat ul Mujahideen in March 2007. (dpa)