The top separatist group in India's Assam state says it was behind attacks on pipelines which oil officials say have critically damaged operations.
Ulfa denies it was behind the marketplace bombing in Boko
But the United Liberation Front of Assam denied it killed four people in a bombing of a marketplace near state capital Guwahati on Sunday.
Police had blamed Ulfa for the bombing at a bus stop in Boko, 40km (25 miles) west of Guwahati.
Ulfa has been fighting for a separate Assamese homeland for two decades.
Analysts say the group often steps up attacks ahead of India's independence day on 15 August.
Assam police intelligence chief Khagen Sarmah told the BBC he was sure the Ulfa was behind all the attacks.
"No other group in Assam has the capacity to set off explosions at such distances within hours of each other in such a synchronised manner, only the Ulfa can do it and they have a reason for doing it now," he said.
The military wing chief of Ulfa, Paresh Barua, told the BBC its fighters had carried out the pipeline attacks.
He said the fighters "would continue to attack Indian economic and military targets" but on the Boko bombing said: "There was no reason why we should kill our own people."
He said: "Government agents are throwing grenades and bursting bombs in crowded markets to defame us and confuse our people."
An attack on Sunday at Chellakapar, in Assam's northern district of Sibsagar, destroyed part of a pipeline of the state-owned Oil India Limited.
About 12 armed rebels overpowered the guards at midnight and set off explosives by remote control.
It took several hours to control the fire and it would take a few days to repair the pipeline, said general manager (services) of Oil India, AK Bhandari.
The head of Oil India's operations in Assam, GK Talukdar, told Associated Press: "Our production is on, but our storage capacity is going down, and our operations are turning critical."
Analysts say efforts to open a dialogue between the Indian government and Ulfa have almost fallen through after Delhi refused to release 10 senior rebel leaders.
"If [Delhi] is sincere about talks, our senior leaders should be released so that we can form a consensus within our organisation about how to go about the talks," Mr Barua said.