* Asia to get 2-3 more ESPO cargoes a month after Russian refinery fire
* Abundant crude supply, weak refining margins weigh on ESPO premiums
* Buyers cautious after tougher U.S. sanctions on Rosneft
By Florence Tan and Jacob Gronholt-Pedersen
SINGAPORE, July 18 (Reuters) - Russia is offering more crude oil for exports to Asian markets after a fire at a refinery near its Pacific coast, though the higher supply and nervousness about the impact of tougher sanctions on Moscow over Ukraine is weighing on prices.
Additional Russian supply will give Asian refiners more options on their crude mixes, intensifying competition with rival Middle East grades, at a time when they are already processing less oil amid low profits and slow seasonal demand.
Fresh U.S. sanctions against Russian companies this week could also prompt some buyers to shy away from the grade and put pressure on the main marketer of Eastern Siberian-Pacific Ocean (ESPO) oil, Rosneft, to lower prices, traders said.
"People who want to buy ESPO may go to other suppliers, and Rosneft might struggle to find buyers for their cargoes," said a trader with a refinery in North Asia. Other sellers of the grade include Surgutneftegas, Gazprom Neft and Lukoil.
"We will try not to touch if possible, as we need to observe the situation carefully," the trader said.
Russia could ship an extra 1.2 million tonnes of ESPO oil from the Pacific port of Kozmino this year, dumping it into a market already flooded with crude.
The new export volumes - due to a fire that halted output at Russia's Achinsk refinery in June - will amount to two or three 730,000-barrel cargoes each month until the end of the year. This would be on top of the 19 or 20 cargoes per month the port plans to export this year.
Asian buyers have reacted by bidding premiums for ESPO crude to their lowest in more than a year. Japan, China and South Korea are the top ESPO buyers.
State-controlled oil producer Rosneft sold a cargo this week loading in late-August at $2.65 a barrel above Dubai quotes, down from other August-loading cargoes that earlier brought premiums ranging from $3.50 to $4.40 a barrel.
The new sanctions imposed this week by Washington in effect close medium- and long-term dollar funding, the Treasury Department said. U.S. companies are now prohibited from engaging in any "new debt of longer than 90 days maturity or new equity" with the energy firms and banks.
Traders and analysts said trade financing, required to cover Rosneft's trading operations, comes in well below that period.
The sanctions, though, may cause banks to be more cautious on financing deals that include Rosneft, said a second trader with a refinery in North Asia.
The downing of a Malaysian airliner over eastern Ukraine also raises the possibility that up-to-now reluctant Europeans may get behind tougher "sectoral" sanctions long-sought by the United States.
"I'm not sure if some companies will want to work with (Rosneft)," said a Singapore-based trader.
Others were sceptical that ESPO could be impacted by the sanctions.
"Refiners need ESPO, so they will continue to buy as long as it's not prohibited, but they would have to persuade banks that there's currently no problem," a third trader said.
Russia began production of ESPO crude at newly developed fields in eastern Siberia in 2009. The sour grade quickly became popular among Japanese, Chinese and South Korean refiners as an alternative to Middle Eastern grades due to its proximity. (Reporting by Jacob Gronholt-Pedersen and Florence Tan; Editing by Tom Hogue)