* PTT to buy 1 mln tonnes/year in 2017 and 2018
* PTT to buy 1.2 mln tonnes/year from 2019
* Raises long-term LNG purchase to meet rising demand (Adds details on long-term LNG purchase plan)
BANGKOK, Dec 8 (Reuters) - Thailand's energy policy committee has approved a proposal for state-owned PTT Pcl to buy liquefied natural gas (LNG) from Malaysia's Petronas over a 15-year period, a senior energy ministry official said on Thursday.
PTT will buy 1 million tonnes of LNG per year from Petronas in 2017 and 2018, and 1.2 million tonnes from 2019 onwards, the committee said in a statement.
The plan is subject to Cabinet approval and the draft contract will be examined by the Office of the Attorney General, the director-general of the ministry's Energy Policy and Planning Office, Twarath Sutabutr, told reporters without giving an exact time frame.
Petronas will be Thailand's fourth LNG supplier under long-term contracts.
PTT, Thailand's sole gas supplier, has already signed a 20-year contract to buy 2 million tonnes of LNG a year from Qatar that came into effect last year.
PTT recently won approval to sign long-term contracts with Royal Dutch Shell and BP to buy 1 million tonnes LNG each per year. The contracts are expected to be signed within this year.
Thailand uses natural gas for nearly 70 percent of its power generation. The country has become increasingly reliant on LNG imports as its own domestic gas fields are being depleted.
The committee said on Thursday that it had also approved a new LNG import plan for the next 20 years to meet rising demand after delays in the construction of coal-fired power plants.
Thailand recently revised its LNG imports target to 17.4 million tonnes in 2022 and reaching 34 million tonnes a year by 2036, up from earlier planned 31 million tonnes.
PTT is already in the process of doubling the capacity of its existing LNG import terminal to 10 million tonnes, which will be completed in 2017, and another expansion of 1.5 million tonnes, to be completed in 2019.
The energy planning committee last month approved PTT's plan to raise the capacity of its new LNG import terminal to 7.5 million tonnes a year from 5 million, with an estimated cost of 38.5 billion baht ($1.08 billion). ($1 = 35.6000 baht) (Reporting by Pracha Hariraksapitak and Orathai Sriring; Writing by Amy Sawitta Lefevre and Khettiya Jittapong; Editing by Muralikumar Anantharaman and Subhranshu Sahu)