Eight officers were killed in a landmine blast blamed on Maoist rebels in the northern state of Jharkhand.

They blasted the building, which has totally collapsed, but the train track is still safe

P Krishnaya, rail spokesman

In Manipur state in the north-east, separatist rebels shot dead seven policemen.

Earlier, a railway station in southern Andhra Pradesh state was bombed, although no one was injured.

Two days ago, 14 passengers lost their lives in Andhra Pradesh when suspected Maoists blew up the bus they were travelling on.

Calm ends

The mine attack in Jharkhand took place in Latehar district, police say, about 110 kilometres (70 miles) north-west of the state capital, Ranchi.

Many are still critically injured after the bus attack

A senior police official told the BBC the blast occurred near a road bridge. All the members of the police patrol died at the scene.

No group has said it carried out the attack.

The clash in Manipur was the first major attack since state elections in February, and could signal an upsurge in violence, officials fear.

Rebels opened fire on a police convoy on a road leading to a major hydro-electric project at Logtak.

Police suspect the involvement of the outlawed United National Liberation Front, which wants independence for Manipur from India.

Told to go

Rail services in Andhra Pradesh, meanwhile, have been severely disrupted following the attack in Guntur district, some 250 kilometres (155 miles) east of Hyderabad.

The authorities say about 40 armed rebels stormed Tummala Cheruvu station early on Wednesday.

They blew up signalling and communications equipment after telling staff to leave.

"They blasted the building, which has totally collapsed, but the train track is still safe," railway spokesman P Krishnaya told the AFP news agency.

Both this incident and Tuesday's bus attack have been blamed on the Maoist People's War Group.

It has been fighting a campaign against the authorities and landowners in five neighbouring states for more than 20 years.

More than 6,000 people have died in the struggle.