Police on Friday claimed they had made a major breakthrough in their probe into recent attacks on Hindi-speaking people by United Liberation Front of Asom militants with the arrest of a rebel behind the first wave of strikes at Longswal village on January 5 that left seven people dead.

Tinsukia District's Superintendent of Police Prasanta Bhuyan told PTI in Dibrugarh that hardcore ULFA militant Dhruba Kujur, who belonged to the its '28 battalion', had masterminded and carried out the attack.

A series of orchestrated attacks by ULFA followed in the districts of Tinsukia and Sibsagar that left over 70 migrant workers dead.

Bhuyan said Kujur, arrested from an area under Makum police station, confessed to having planned the attack in Longswal with four of his associates on January 4.

Police in Tinsukia conducted a search at Mamoroni village and unearthed a huge amount of arms and explosives of ULFA from the house of 'link-man' Pilingia Moran, Bhuyan said.

Two kg of TNT, capable of making 17 powerful bombs, 2 huge remote-controlled explosive devices, 17 detonators and some fuse wires were seized by police.

Pilingia Moran is absconding, he said.

Three alleged 'link-men' of ULFA were arrested as the army continued its 'Operation Clear' to flush out cadres of the banned group from Upper Assam.

The army has moved deep in forests along the Assam-Arunachal Pradesh border and reserve forests in the two states, seeking rebels responsible for the recent killings.

According to army sources in Dibrugarh, three alleged ULFA link-men led by Tarun Mahanta were arrested on Thursday night in Bandarkati, Doomdooma and Kakopathar areas of Tinsukia district. A grenade and seven rounds of AK-56 ammunition were seized from them, they said.

Intensive operations had been launched to flush out the rebels from camps in Tirap, Changlang and Lohit districts of Arunachal Pradesh and Dibru Saikhowa and Lakhipathar reserve forests in Assam, the sources said.

Troops have fanned out to the forest villages of Nagajan, Mothola, Dimukhula, Laila and Sumuguri to conduct house-to-house searches.

The army said a platoon of the Border Security Force was deployed in areas of Tinsukia and Sibsagar districts with sizeable populations of Hindi-speaking people employed in brick kilns.