Ayanjit Sen BBC reporter in Delhi

The Home Ministry in Delhi said the illegal immigrant issue had to be tackled with ''utmost urgency''.

In a statement issued after a day-long security meeting of top Indian officials, the ministry said: ''The presence of a large number of illegal foreign immigrants, particularly from Bangladesh, poses a serious threat to internal security.''

However, the Bangladeshi authorities have dismissed the Indian statement as "absurd. "

A Foreign Office spokesman in Dhaka said no Bangladeshis were in India illegally.

More than half the estimated Bangladeshi immigrants in India live in the north-eastern state of Assam or the eastern state of West Bengal.

Presence denied

Bangladeshi Foreign Secretary Shamsher Mobin Chowdhury told the BBC his office would only give a reaction after an official confirmation of the ministry's statement.

However, Bangladeshi governments have consistently denied the presence of any illegal immigrants in India.

An Indian home ministry spokesman said the deportation drive was expected to begin between April and June.

A few Indian states, including Uttar Pradesh and Rajasthan, have already launched a drive to identify immigrants from Bangladesh.

A few months ago, the Rajasthan government said Bangladeshi nationals who were staying illegally would be deported.

The move followed a clash between Bangladeshi immigrants and police in the state capital, Jaipur.

India and Bangladesh share a 4,143-kilometre border.

India says it has already begun constructing barbed-wire fences to stop smuggling and infiltration, mostly by Muslim settlers, along the border in Assam, West Bengal and Tripura.