The Thai government and Muslim separatists in the south of the country have announced they will stop fighting each other during the Muslim fasting month of Ramadan.
The conflict has killed more than 5,000 people in the last decade.
The agreement is the first major step since February, when the two sides signed a first-ever peace talks deal.
Malaysia is facilitating the negotiations but correspondents say that progress has been slow.
Attacks in the region have occurred almost daily despite several rounds of talks since March.
Mediator Ahmad Zamzamin Hashim said that both parties had "reached a common understanding to work towards a violence-free Ramadan".
Under the terms of the "Ramadan Peace Initiative", Thai security forces will refrain from "aggressive actions" while rebel groups including the Barisan Revolusi Nasional (BRN) will not engage in "armed attacks, bombings and ambushes" against Thai troops.
"This is a stepping stone to what we want to achieve in the future. If there are no incidents, we can see the light at the end of the tunnel. It will be a precedent, a stepping stone," Mr Hashim said.
The deal is for a 40-day period from 10 July to 18 August and will be effective in the southern provinces of Yala, Pattani, Narathiwat and Songkhla, he said.
Thailand's National Security Council chief and lead peace negotiator Paradorn Pattanatabut welcomed the rebels' pledge, but warned that some splinter groups were opposed to dialogue.
"But I'm convinced that the BRN will be able to curb violence," he told the AFP news agency in Bangkok. "In the past they never came out and made a clear announcement of their goal."
The BBC's Jennifer Pak in Kuala Lumpur says that it has been a shaky peace process and that the deal is a verbal agreement - nothing has been signed.
Our correspondent says that the worry is that the negotiators representing rebel groups do not have full command of their troops.
But the peace talks are different from previous attempts because this is the first time that the Thai state has recognised the insurgents and is allowing their demands to be heard and discussed.
Thai negotiators have suggested the possibility of creating some form of locally-elected administration in the region, but full autonomy for the south remains off the agenda because the Thai constitution stipulates that the Buddhist-majority kingdom must not be divided.