The army on Monday shot dead four United Liberation Front of Asom militants in Betgaon Kagramari village under Tangla police station of Udalguri district, northern Assam even as security forces and police mounted an operation against the group before its raising day on April 7.

Security sources informed that the militants were killed following an encounter on Monday afternoon. A red alert was sounded all over the state fearing attacks by the militant group in the run up to its raising day on April 7.

The banned ULFA was formed on April 7, 1979, in Sivasagar district of Upper Assam.

The militants are used to carrying out attacks on security forces and vital installations, including oil installations in eastern Assam on or before April 7 to mark its raising day.

Meanwhile, chairman of ULFA Arabinda Rajkhowa in an e-mail on Monday called for a 12-hour state-wide bandh from 6 am on April 4 in protest against 'atrocities' perpetrated by Assam police on the fasting wives of six ULFA leaders who had allegedly gone 'untraced' in December 2003 following their hand over to India by Bhutan after they had been captured by Royal Bhutan Army during Operation All Clear, aimed at demolishing the ULFA base in the neighbouring country.

The six wives of 'missing' ULFA leaders were on indefinite fast in Guwahati since March 21 demanding information on the whereabouts of their 'missing' rebel husbands.

They were arrested on March 30 by the police on charges of 'attempt to commit suicide' and admitted to Guwahati Medical College Hospital where they are being administered saline drips.