* Slower pace of US corn, soybean harvest supports prices
* Wheat market firm on good demand, Black Sea risks
* Ample global grain supplies still keeping lid on futures
PARIS/SINGAPORE, Sept 26 (Reuters) - Chicago wheat extended gains on Tuesday, underpinned by export demand and risks to Black Sea supplies, while soybeans also held firm with support from a slower-than-expected U.S. harvest pace.
Corn inched down after earlier reaching its highest in over a week.
Ample global supplies continued to cap grain prices while participants were also looking ahead to quarterly U.S. stocks data on Friday for further direction.
The most-active wheat contract on the Chicago Board of Trade (CBOT) was up 0.4% at $5.91-1/4 a bushel by 1157 GMT. The market was higher for a third straight session as it recovered after approaching a near three-year low last week.
Latest Russian attacks on Ukrainian ports have created doubts about Ukraine's export capacity, while an unofficial minimum price for Russian wheat exports was also raising questions about Black Sea supply.
Offers reported by traders in an import tender being held by Tunisia on Tuesday showed large Russian grain houses were absent.
"This (Tunisian tender) will once again fuel discussions around the unofficial but much-discussed Russian price 'floor'," consultancy Agritel said.
"The weather market in the southern hemisphere and persistent tensions over Ukrainian port infrastructure are other factors dominating the news," it said in a note.
Large Russian exports since July had pressured international prices, despite the collapse of a Black Sea grain deal allowing shipments from Ukraine's sea ports.
But with drought threatening to reduce harvests in Argentina and Australia, uncertainty over Black Sea supply was stirring concern about export availability later in the season.
CBOT corn was down 0.3% at $4.79-3/4 a bushel after earlier touching its highest in over a week.
Soybeans ticked up 0.3% to $13.02 a bushel as it moved away from a six-week low struck on Monday.
After Monday's close, the U.S. Department of Agriculture (USDA) reported that soybean and corn harvests advanced more slowly last week than analysts had expected.
After weekend showers held up field work, parts of the Midwest are forecast to see more showers in the week ahead, though the moisture may help later-developing crops after hot, dry spells this year.
"There is support for corn and soybean prices because of some issues with the U.S. harvest," said one Singapore-based trader. "But it is still early to be too much worried about the harvest." (Reporting by Gus Trompiz in Paris and Naveen Thukral in Singapore; Editing by Subhranshu Sahu and Mark Potter)
