The Indonesian army has orchestrated mob attacks on international peace observers and civilians in Aceh, according to human rights observers in the strife-torn province.
Indonesia is increasing its military presence in Aceh
A member of the rights organisation Kontras told the BBC that the Indonesian army had been training "East Timor-style militias" in order to destroy a fragile peace agreement in Aceh.
A senior Indonesian official denied the claims, and blamed rebels from the Free Aceh Movement (GAM) for undermining the peace process.
Speaking to the BBC's East Asia Today programme, Kontras spokesman Samsul said that the Indonesian army was deliberately trying to break down the peace process.
"There are three groups of people perpetrating violence in Aceh: the Indonesian army and police force, GAM and Indonesian-trained militias," he said.
Samsul said that the militias have been trained by the Indonesian police and army since the year 2001.
"In central Aceh they attacked the international peace monitoring team, they burned the offices in East Aceh," he said.
"All this is committed by the militias. We are now facing the same situation that happened in East Timor," he said, referring to 1999 violence which left 1,000 people dead and which was blamed on militias with Indonesian army backing.
But Benny Suryawinata, Indonesian deputy co-ordinating minister for security, denied the claims.
"It is not true. It is all biased and one-sided," he said.
"If you go to Aceh itself, you can see how GAM treats the Acehnese people. The accusations are not true."
He also denied that the Indonesian government or military were seeking to undermine the peace process.
"The Indonesians are willing to negotiate with GAM. It is GAM who is not serious about negotiation, " he said.
The Indonesian government has given GAM a deadline of 12 May to accept its conditions for talks aimed at saving the peace deal.
But the BBC's Jakarta correspondent Rachel Harvey says the situation on the ground is deteriorating rapidly. Violent incidents are on the increase, with thousands of villagers fleeing their homes and seeking refuge in local mosques and schools.
Speaking to Indonesian troops in the city of Surabaya, military commander Endriartono Sutarto told several thousand troops that they should ready themselves for a war in Aceh.
"The government of Indonesia's priority is a bloodless resolution, but GAM had refused to honour that stance," he told the marines.
"If they don't surrender their weapons, then the Indonesian army will fight them with its weapons," he said, according to the Reuters news agency.
GAM and the Indonesian government signed a peace agreement in December last year, which was designed to end the 26-year conflict which has claimed at least 12,000 lives.
Under the terms of the agreement, the rebels were supposed to place their weapons in special arms dumps, and the Indonesian military was meant to withdraw to defensive positions.
Neither Jakarta nor GAM has so far fulfilled its side of the bargain, and both sides continue to blame each other for the breakdown in relations.