(Recasts with Russia clarification on ban duration)

By Pavel Polityuk and Denis Dyomkin

KIEV/MOSCOW, Sept 7 (Reuters) - Major exporter Ukraine isholding ships carrying a month's grain supply in its ports,traders said on Tuesday, while Russia said it had enough grainto feed itself but would maintain an export ban until late 2011.

The Russian statement could bring some clarity andreassurance to a market frustrated by conflicting statementsfrom a country that before this summer's record heatwave andresulting drought was the world's third largest wheat exporter.

Ukraine's Customs Service, reacting to lower harvests aftersevere weather and increased demand in the absence of Russiansales, has blocked in ports 24 vessels bound for export carrying379,647 tonnes of grain, mostly wheat, traders' union UZA saidin a statement on Tuesday. "According to the latest data, about 20 ships are staying inports without official explanations. Some of the ships have beenin port for more than one and half months," UZA said.

But traders said the real volume of grain held back at portscould be much higher.

"The data provided by UZA is just a tip of the iceberg andthis is just 25 percent of the real volume. UZA counts ships oflarge exporters only, while there are also many ships of smalltraders in ports," a large Ukrainian trader told Reuters.

The Ukrainian government last month proposed limitingexports of the two key commodities wheat and barley to 2.5million tonnes between September and December but has put off afinal decision until October.

RUSSIA OFFERS SOME CLARITY

Russia on Tuesday sought to remove uncertainty over the fateof its grain export plan, with the Kremlin clarifying that theembargo -- introduced on Aug. 15 and originally slated to end onDec. 31, 2010 -- would remain in place until after next year'sharvest has been collected.

The statement followed Russian President Dmitry Medvedev'scomments on Monday that the export ban might be lifted earlierthan the end of this year, which appeared to contradict PrimeMinister Vladimir Putin, who has said it may be extended to late2011..

"When speaking about the possible cancellation of the ban onthe export of grain, the president meant next year's harvest,"the Kremlin spokesman told reporters.

The clarification should be welcomed by traders, who hadbeen frustrated by a string of conflicting statements fromRussia and the resulting see-saw moves in grain prices.

However the size of Russia's grain stocks -- and whether itwould need to import wheat this year -- remained unclear.

Agriculture Minister Yelena Skrynnik said Russia had enoughgrain to feed itself, revising up the carry over grain stocksestimate to 26 million tonnes from 21.7 million. This appearedto contradict Medvedev's comments on Monday that the countrywould need to look for grain -- which are also in line withanalysts' expectations.

The Kremlin and top economic officials have been at pains toreassure the public, already feeling the inflationary effects ofthe drought and worried about shortages.

"There will be enough grain for food and for the feeding ofanimals," Interfax news agency quoted Skrynnik as saying.

Russia plans to harvest 60-65 million tonnes of grain in2010 compared to 97 million in 2009, and, according to officialestimates needs around 77 million tonnes to meet domestic needs.

NO REPEAT OF FOOD RIOTS?

Ukrainian agriculture officials have said that turmoil on thelocal grain market is a result of Russia's decision to banexports after its record drought slashed grain crops.

They said foreign traders could accelerate grain exportsfrom Ukraine in a bid to cover an absence of Russian produce onthe world's market and this could leave Ukraine without enoughwheat to cover local needs.

Uncertainty about Russia's grain output and the duration ofits export ban had sent prices soaring on international grainmarkets, with key wheat prices hitting two-year highs early inAugust, although well below 2008 levels when concerns over foodshortages sparked riots in a number of countries.

Analysts said Egypt, a major buyer of Russian wheat forcedto look elsewhere for grain, was unlikely to face 2008-styledisorder over food supplies.

"I do not see the situation escalating to public unrest andriots similar to what happened in 2008, because internationalwheat prices are not rising to 2008 levels," said Magdy Sobhy atthe Al Ahram Centre for Political and Strategic Studies.

The UN's Food and Agriculture OrganisationAssistant-Director General Hafez Ghanem reiterated FAO commentslast week that the world was not headed for a repeat of the2007/2008 food crisis and said the international communityshould act together to tackle future volatility.

"Given the importance of food markets in fighting hunger andensuring economic stability FAO feels that the internationalcommunity, perhaps under the leadership of the G20, should startlooking at ways of dealing with higher volatility," he said.

The FAO has called an emergency meeting for Sept. 24 in Romefor governments to confront weaknesses in the global food systemand find ways to boost reserves. (Writing by Toni Vorobyova; additional reporting by AleksandrasBudrys; editing by Keiron Henderson)