* Crude oil prices are near 3-year highs
* Thermal coal at highest seasonal level in half-decade
* Asian LNG market has gradually tightened since 2016
By Henning Gloystein and Oleg Vukmanovic
SINGAPORE/LONDON, May 4 (Reuters) - Asian spot prices for liquefied natural gas (LNG) firmed over the past week, supported by strong oil and coal markets and amid a structural tightening of the fuel's fundamentals.
Asian LNG prices for delivery in June LNG-AS were at $8.1 per million British thermal units (mmBtu), up 15 cents from last week's value and more than 15 percent above a seasonal low from early April.
Traders said prices remained firm despite LNG markets being in the midst of the northern hemisphere's low-demand spring season, during which little gas is used.
"LNG prices are being supported by external factors, namely oil and coal," said one Singapore-based trader.
Crude oil prices , to which gas markets are closely linked, are near three-year highs on expectations that the United States will re-introduce sanctions on major exporter Iran.
Asian benchmark thermal coal prices are at their highest seasonal level in more than five years at over $100 per tonne, driven by unexpectedly strong demand.
Coal and gas markets are linked as they are the main fossil fuel competitors in power generation.
Overall, the LNG market in Asia has tightened over the past year, with the winter seasonal demand peak (December/January) and spring low (April/May) seeing significantly higher prices in 2017/2018 than in 2016/2017.
Booming demand for LNG is also visible in the shipping sector, where hundreds of new LNG tankers are being built.
"Over the 2018-2022 period, 265 LNG carriers are expected to be delivered, as record numbers of carriers will be required to meet the increased LNG output expected by the end of the forecast period," said energy consultancy Westwood.
In physical markets, Taiwan's state utility CPC bought LNG for June via a tender for about $8.30 per mmBtu, traders said.
South Korea's SK Energy is seeking a cargo for early June and July delivery, while India's Gail awarded 12 LNG cargoes to Dominion Energy's Cove Point LNG export facility in the United States this week.
Cove point started exports in March and is the second U.S. LNG export facility after Cheniere's Sabine Pass in Louisiana.
In Africa, Cameroon is preparing its first LNG cargo from the Golar LNG-built Hilli Episeyo Floating LNG facility, with the Galicia Spirit tanker due to load.
Angola also issued an LNG export tender this week.
In the Caribbean, Trinidad & Tobago issued a tender for cargo loading on June 8, traders said.
Reporting by Henning Gloystein in SINGAPORE and Oleg Vukmanovic in LONDON; Editing by Tom Hogue