* Japan crude imports from Iran fall 19 pct in Oct to 127,279
* Japan's Jan-Oct imports almost unchanged at 188,000 bpd
* Top Asian buyers Jan-Oct imports fall 15 pct, slump 43 pct in Oct
TOKYO, Nov 29 (Reuters) - Asia's top buyers of Iranian crude cut purchases by about 15 percent so far this year but shipments may start rising after six world powers agreed this past Sunday to ease some sanctions on Iran in return for curbs on its nuclear programme.
Tough U.S. and EU sanctions have slashed exports from the OPEC member by more than half to about 1 million barrels per day (bpd), costing it as much as $80 billion in lost revenue since early 2012, according to White House estimates.
That pressured Iran to the negotiating table with world powers, resulting in a historic deal on Nov. 24 that gives Tehran some relief for its shattered economy.
India has already said it might start buying more crude from Iran because it has cut its imports below what was allowed by sanctions. Iran can also transfer some of the billions in petrodollars that have been held up in purchasing countries.
"Buyers like India really couldn't take much Iranian oil because of issues surrounding insurance," said Tony Nunan, oil risk manager at Mitsubishi Corp in Tokyo.
"The deal smoothens out things a bit, and that will make it easier for buyers to import Iranian oil. We may see some increases in exports," he said.
Imports by Iran's largest customers - China, India, Japan and South Korea - dropped to 924,560 bpd in the first 10 months of the year, down from 1.087 million bpd in the same period a year ago, according to official customs reports and tanker data from trade sources.
Shipments in October by the four totalled 669,524 bpd, down 42.6 pct from 1.17 million bpd a year ago.
India made the deepest cuts this year as two of its state-run refiners worried about constraints to insurance coverage for tankers carrying Iranian oil and refineries processing it.
Although the Geneva deal doesn't allow Iran to boost oil sales for six months, India has room to raise its imports after cutting them about 40 percent so far this year to 193,900 bpd.
India may buy more crude from Iran in the next four months and intends to increase purchases further in the next fiscal year, its top oil bureaucrat said on Wednesday.
Underlining the depth of Iran's pain from the sanctions, its biggest customer China imported just under 250,000 bpd of Iranian crude in October, the lowest level since June 2010.
In the first ten months, China's purchases from Iran were down 3.4 percent at 409,976 bpd.
Japan, which has struggled to cut its Iranian crude purchases this year after reducing them more than 40 percent in 2012, imported 127,279 bpd in October, down 19 percent, the country's trade ministry said on Friday.
Japan's imports of the oil were almost unchanged for the 10 months through October at about 188,000 bpd, the data showed.
South Korea's imports of Iran oil fell 9.2 percent to 132,648 bpd between January and October.
The U.S. believes the economic impact on Iran from its and the EU's sanctions forced Tehran to the negotiating table, and Washington has stressed that Tehran has to take concrete steps within six months for further easing of the measures.
The European Union and the United States believe Iran is developing nuclear weapons, while Iran says its programme is for power generation.
Iran is quietly mobilising more ships to store and transport oil, aiming to keep its fields working and mitigate losses while the sanctions remain in place.
"It's not like Iranian exports will jump by another 1 million bpd straightaway," said Nunan. "That's why apart from the huge fall in oil we saw on Monday, prices have stabilised and are moving sideways."
The United States, which grants sanction waivers to buyers who continually reduce their purchases from Iran, is due to review compliance by China, India and South Korea soon.
Government and refinery officials in India have said they believe the grant of the next six-month waiver is a formality after the Sunday deal between the world powers and Iran.
Iran's oil sales were expected to fall sharply in October to their lowest in months at about 719,000 bpd, according to sources who track preliminary tanker loading plans.
(Additional reporting by Manash Goswami; Writing by Aaron Sheldrick; Editing by Tom Hogue and Simon Webb)