He said the gunmen on a motor-cycle fired from automatic rifles at a car carrying Sarkar, a member of the CPI-M State committee, and his two supporters at Subhasnagar killing them instantly.

The MLA's bodyguard was wounded and his condition was stated to be critical.The attack on Sarkar, who was on his way to attend a party meeting, came barely 18 hours after unidentified gunmen shot dead former Bihar minister Brij Bihari Prasad and his bodyguard here.

And to compound mattes further, six persons, including Samata Party MLA from Govindganj, Bhupendra Nath Dubey, were named accused in connection with the killing of Prasad.

This has forced the police to go on maximum alert. A general alert was also sounded in Bihar following the killing of these two politicians in quicksuccession.

The DGP said police had been asked to provide extra security to those Members of Parliament and State Legislature facing threat to their lives.The situation in Purnea was tense but under control, Jacob said.

CPI-M State secretary Ganesh Shanker Vidyarth condemned the killing of Sarkar, who was elected to the Legislative Assembly four times since 1980 from Purnea, and demanded dismissal of the Rabri Devi government.

He said the State government had lost its moral authority to govern following the killing of two politicians. The Centre should not delay dismissal of the Rabri Devi government, Vidyarth said.

However, Rashtriya Janata Dal president Laloo Prasad Yadav lashed out at Opposition parties demanding President's rule in Bihar following the twin murders.

Opposition parties, including BJP, Samata Party, Janata Dal besides Left Parties have demanded immediate dismissal of the Rabri Devi government.Talking to newsmen, Laloo Yadav said the law and order situation in the State was ``quiteunder control'' and termed the demand for dismissal of ``a duly elected'' government as ``politically motivated and unconstitutional''.

Laloo Yadav said the murders were part of ``a deep-rooted'' conspiracy as it took place ``despite presence of a large number of security guards''.He said a high-level official inquiry would be instituted to go into the conspiracy and the culprits would be brought to book soon.

In a related development, Bihar Police today claimed to have got ``vital clues'' to the killing of Bihari Prasad. DGP Jacob told newsmen that security lapse in the case could not be ruled out and the matter is being ``thoroughly investigated''.

A taskforce has been constituted to study the case and intensify the combing operation and arrest the killers, he said, adding CID sleuths have been asked to assist it.

Prasad and his security guard Lakshmeshwar Sahu were gunned down during their evening stroll at the compounds of Indira Gandhi Institute of Medical Sciences, where he was lodged injudicial custody in connection with Bihar Combine Engineering entrance test scam.

Meanwhile, six persons, including Samata Party MLA from Govindganj, Bhupendra Nath Dubey, were named accused in connection with the killing of former Bihar minister and sitting RJD MLA, Brij Bihari Prasad.

The FIR was registered by one Amlendu Kumar Sinha of Adapur in Sastrinagar police under Section 302, 307, 34, 120 (b) and 32 of the IPC, police sources said.