Two bombs exploded in a marketplace in Dimapur, commercial centre of the state of Nagaland, while a third ripped through a crowded railway station there almost simultaneously, an officer at the local police station said.

Twenty-six people died in the Nagaland attacks, the deadliest since a ceasefire with the main Naga separatist group began seven years ago.

Later, tribal guerrillas fighting for a separate homeland in the neighbouring state of Assam massacred 11 people. One man died in another bomb explosion in Assam and eight more people were killed in four separate grenade attacks.

Police said the attacks in Nagaland and Assam appeared to be unrelated.

Janardhan Singh, Dimapur's police superintendent, said the attacks in Nagaland were aimed at disrupting the peace process.

Twelve people died at the railway station and eight were killed at the market. Six later died in hospital.

"It was a powerful blast, the tin roof of the railway platform has been blown," railway official Robin Kalita said.

"There are pieces of flesh and torn human limbs lying on the platform. There are people wailing," Yanger Thakkar, a journalist in Dimapur, told Reuters.

The blasts in Christian-majority Nagaland could have been set off by any of several smaller separatist groups that are not part of the truce with the Indian government, officials said.

The biggest group, the National Socialist Council of Nagaland (Isaac-Muivah), which has fought for a separate Naga nation for more than half a century, has held several rounds of talks with government officials but with no breakthrough.