Highly placed sources said Prime Minister Khaleda Zia approved the move against one of her most trusted bureaucrats after he arbitrarily handled an anonymous letter that made allegations of gross corruption against her eldest son and Joint Secretary General of ruling BNP Tarique Rahman.

President Iajuddin Ahmed approved the decision for Islam's instant removal in accordance with Article 9 (2) of the Public Service (Retirement) Ordinance, 1974 that provides for a civil servant's removal on completion of 25 years of service.

A Press Information Department release however said the government forced him into retirement in public interest.

The government meanwhile appointed Acting Education Secretary Khondker Shahidul Islam as the Prime Minister's Acting Secretary.

Nurul Islam told The Daily Star last night that he had not received any letter relating to termination of his service. He also declined to make any comment about the allegations against him and said he attended office yesterday.

Bac launched the probe against him on charge of taking away about 500 files from the Prime Minister's Office (PMO) in 12 CDs.

A Bac team went to his house last night and saw him at a meeting with some top officials and former bureaucrats, including Planning Commission Member Fazlur Rahman and former education secretary Shahidul Alam.

The team asked him to go to the Bac office this morning and give his statement on the CDs.

Sources at the PMO said the acting secretary was put under virtual suspension since Wednesday.

They said Islam came under fire from the prime minister herself as he ordered investigation into a number of allegations of corruption which the anonymous letter made against Tarique.

Islam joined as private secretary to the prime minister with the rank and status of deputy secretary immediately after the BNP-led alliance government took office. He was promoted to the posts of joint secretary and additional secretary in a year before being made acting secretary to the PM.

Islam reportedly joined anti-BNP government platform "Janatar Mancha" in 1996, but he still emerged as one of the most influential officials with the blessing of the head of the government. He is believed to have influenced most of the administrative decisions such as promotion, posting and appointment that the PMO took.

PMO sources said Islam received an anonymous letter addressed to him in early April and issued orders to investigate the allegation on April 20, a day ahead of main opposition Awami League's Hawa Bhaban siege programme.

He also pressed officials of the ministries concerned to complete the investigation and immediately send the report to him. But this leaked out last week and a number of ministers, MPs and ruling BNP leaders brought the matter to the notice of the prime minister on her return from Shanghai and demanded his immediate removal.

After toying with the idea for three to four days, the prime minister finally took the decision to remove him as he secretly initiated a probe against her son and several ministers.

PMO sources said the government usually does not attach importance to anonymous letters, although in some cases it did order inquiries considering the gravity of the allegations.

The previous AL government introduced a provision making it mandatory for officials to inform the prime minister before initiating any investigation on the basis of anonymous letter.

But Islam did not inform either the prime minister or other high-ups at the PMO and unilaterally ordered a probe into the allegations. Later, the letter and relevant files were seized with the help of intelligence agencies and officials, PMO sources added.