police hunting a sniper who was last night feared to have shot dead another victim have received a message warning: "Your children are not safe anywhere at any time."

The chilling threat was apparently discovered by police on Saturday night at the scene of a shooting outside a Virginia steakhouse.

Sources said that the warning contained a demand for millions of dollars.

Montgomery County Police Chief Charles Moose said police "will be responding soon" to the latest message.

On Monday, police asked the sniper to call them, saying investigators had received a message too muddled to understand.

Police Chief Moose has now used four Press briefings to communicate directly with the person believed to be the sniper.

Yesterday morning, bus driver Conrad Johnson, 35, was fatally wounded as he prepared for his morning route in nearby Aspen Hill, the suburban Washington community where the shootings began on October 2.

Twelve other people have been confirmed shot by the sniper in Maryland, Virginia and Washington DC. Nine were killed and three were critically wounded.

Mr Johnson, a father of two, was shot as he stood at the top of the steps of the bus, shortly before 6am.

The shooting happened near an apartment building and wooded area along Connecticut Avenue. The bus was parked at a staging area where drivers get ready for their morning runs.

Police set up a massive dragnet around the area, blocking traffic in and out of Washington.

Agents for the federal Bureau of Alcohol, Tobacco and Firearms combed the crime scene. A police dog searched near a basketball court in a park, and police helicopters flew over the scene.

Earlier, police said two men detained in Richmond, Virginia, on Monday and questioned in connection with the sniper attacks had nothing to do with the case.