SINGAPORE, April 23 (Reuters) - The Asia-Pacific crude market held steady on Wednesday, although ample supply and weak seasonal demand weighed on the market. The premium for Russian ESPO crude strengthened slightly, after Surgut sold 730,000 barrels of the medium sour blend for June 5-10 loading to SK Energy at around $4.65 per barrel above Dubai quotes. ESPO was last sold at a premium of $4.40-$4.50 for cargoes loading late-May and early June, after trading at a $3.90-$4.55 premium last month. Rosneft on Wednesday closed a tender to sell another six cargoes of ESPO crude loading June 10-13, 12-15, 14-17, 21-24, 23-26 and June 25-28. The prospect of increased supply of Vietnamese sweet grade Bach Ho in June as a result of refinery maintenance weighed on differentials for other Vietnamese sweet crudes. Vietnamese state oil marketer PV Oil sold two cargoes of Su Tu Den loading June 1-20 to an oil major and a Japanese firm in a tender at around $2.50 per barrel above dated Brent, down from $4-$4.50 per barrel last month, traders said. The deals could not be verified. Brent-Dubai Exchange of Futures for Swaps (EFS) DUB-EFS-1M, or Brent's premium to Dubai swaps, narrowed 9 cents to $4.08 per barrel. * TENDERS Taiwan's CPC closed a tender to buy 1.9 million barrels of sweet crude. The bids are valid until April 25. Indonesia's Petral closed a tender to buy more sweet crude for June arrival. The company already secured 5.9 million barrels for June arrival. * MARKET NEWS Nigeria has awarded most of its long-term oil contracts worth an estimated $40 billion a year to local companies, according to a confidential list seen by Reuters, meaning global traders need to partner with them to access crude from Africa's top producer. Armed pirates raided a Japanese oil tanker off the coast of Malaysia and abducted three crew members, Malaysian maritime police said on Wednesday, underscoring increasing threats to shipping in one of the world's busiest waterways. China's commercial crude oil inventories at the end of March fell 2.89 percent from a month earlier on lower crude imports, the official Xinhua news agency said on Wednesday. For crude prices, oil product cracks and refining margins, please click on the RICs below.

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