Police have shut down a major highway north west of Washington DC amid reports that two arrests have been made in connection with the hunt for the sniper.

No details have yet been confirmed about arrests or the closure of a stretch of the Interstate 70, a highway close to Middletown, Maryland, about 50 miles (80 kilometres) from Washington DC.

Police told reporters they were planning to hold a news conference on Thursday morning local time.

The reported arrests come after US authorities issued an arrest warrant for two men wanted for questioning in connection with the sniper attacks, which have killed 10 people in the Washington DC area.

Police said they were looking for John Allen Mohammed, also known as John Allen Williams, and his stepson. Officers said they were both armed and dangerous.

John Allen Mohammed is said to be armed and dangerous

It is believed the men may have information about the sniper attacks, but Police Chief Charles Moose warned "not to assume they were involved in the shootings".

Chief Moose also issued another direct message to the sniper during a news conference.

Yard searched

Earlier, FBI agents conducted a major search at a house in Tacoma, Washington state, which is 3,200 kilometres (2,000 miles) from the capital.

Mr Mohammed is believed to have served in the army at a base near Tacoma and to have lived in the house.

Fort Lewis, to the south of the town, provides some of the most intensive sniper training in the US military, correspondents say.

Let's talk directly - We have an answer for you about your option

Message from police

Local television has shown FBI agents and other officers searching the yard of a house in Tacoma with metal detectors and chainsaws, combing the soil and a large tree stump in an apparent search for bullets and metal fragments.

"It looks like an archaeological dig there with tapes running the full length of the yard," one resident said.

A spokesman for Fort Lewis base could not confirm if Mr Mohammed had lived at the address.

	:	Trail of terror
Map showing location of recent attacks

In another development, police are investigating a possible link between the sniper and a killing in Montgomery, Alabama, according to the news agency AFP.

A 52-year-old woman was shot and killed outside a liquor store there on 21 September. Another woman was wounded.

Folk tale clue

At the press conference late on Wednesday, Chief Moose delivered a cryptic message.

"You asked us to say, 'We have caught the sniper like a duck in a noose'. We understand that hearing us say this is important to you. However we want you to know how difficult it has been to understand what you want."

Chief Moose: another direct appeal to killer

The reference to a duck and noose apparently comes from a folk tale, in which a rabbit attempts to catch a duck in a noose but ends up thwarted by the duck, according to the Washington Post.

"Let's talk directly," the police chief continued.

"We have an answer for you about your option. We are waiting for you to contact us."

That may refer to the snipers' demands for $10m apparently left in a note at the scene of one of the shootings.

Since 2 October, 10 people have been killed and three others wounded in Maryland, Virginia and Washington DC in apparently random attacks.

'No expense spared'

The US Government has agreed to give $600,000 to schools in the area to strengthen security.

President George W Bush said local police would have "the full resources of the federal government" to help catch the killer.

"There is a ruthless person on the loose. We pray for a quick end to this period of violence and fear," he said.

Police confirmed on Wednesday that 35-year-old bus driver Conrad Johnson, shot on Tuesday morning, was the sniper's latest victim.

In their appeal for witnesses, police have stressed that any immigrants should not hold back information for fear of police investigating their status.

Chief Moose has offered to set up a private post office box "or another secure method" for the sniper to contact police.