Gauhati, India ? Militants bombed utilities, a tea plantation and a crowded marketplace in northeastern India on Sunday, intensifying violence that has killed 57 people in two days and snarling efforts to bring cease-fires in a region where dozens of ethnic rebel groups are fighting for separate homelands.

At least 17 bombings and shootings were carried out over the weekend in Nagaland and Assam states. The attacks, particularly an explosion Saturday that ripped through a railway station full of commuters, angered even some separatist leaders.

Nearly 40 groups have been fighting in the mountainous region of multiple ethnicities wedged between Bangladesh, Bhutan and Myanmar. Rebels in Nagaland have been leading one of Asia’s longest running separatist conflicts, dating to shortly before India gained independence from Britain in 1947.

Assam’s top police official blamed the string of attacks on two militant groups — the United Liberation Front of Asom and the National Democratic Front of Boroland.

“The entire string of attacks was a joint operation by the ULFA and the NDFB,” Inspector-General Khagen Sarma told The Associated Press. Sunday was the 18th anniversary of the NDFB, which is demanding a homeland for Boroland, a region that straddles both states.

On Friday, the government offered a cease-fire to the Boroland rebels, part of their efforts to tame the various groups.

Insurgent groups in India’s northeast are pushing demands ranging from independent homelands to autonomy within the nation. The rebels say they are seeking to protect their ethnic identities and allege that the federal government has exploited the resources in the mineral- and oil-rich region.

The Indian government denies the allegation and has already signed peace agreements with several groups. In return, the former militants have been given jobs and limited administrative control within the Indian nation.

A bomb exploded late Sunday near a market in Bijni, 125 miles west of Assam’s state capital of Gauhati, leaving three dead. Shortly afterward, another explosion killed another man and left 25 injured in nearby Gauripur along India’s border with Bangladesh.

Guerrillas set off a bomb at a tea plantation in nearby Borhat, killing a worker and wounding two others.

Also in Borhat, suspected rebels targeted government-run Oil India Ltd.’s natural gas pipeline with a land mine blast. The extent of damage was not immediately known.

Two suspected Boroland rebels were killed when explosives they were carrying detonated in Assam’s Sonitpur district, Press Trust of India reported.

A bomb also went off in a market in Dhekiagula, a village 105 miles north of Gauhati, wounding 15 people.

Another bomb wounded a shop owner at Dabosal in western Assam, said A.K. Bhutani, the district magistrate.