UPDATE 1-Poor Afghan security risks election fraud, ICG says

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(Adds U.S. national security adviser, paragraphs 6-7, 18)

By Sayed Salahuddin

KABUL, June 25 (Reuters) - Poor security in the east and south and a failure to capitalise on gains made after a 2004 poll will make it more difficult for Afghanistan to stage a meaningful presidential election on Aug. 20, a leading think tank has said.

Afghanistan's Taliban-led insurgency, which the U.S. military says has hit its most violent level since the Islamist group's ousting in 2001, increases the chance of fraud in the nation's second presidential poll, the International Crisis Group said.

"Security conditions may make it difficult for people in areas of the south and east to exercise their franchise and could also provide the cover for mass fraud," the Brussels-based group said in a statement released overnight.

The election is seen as a crucial point for both Kabul's Western-backed government and for Washington, which has identified Afghanistan as its top military priority and has already almost doubled the number of its troops from the 32,000 in the country in late 2008.

Many of those extra troops will provide security for the poll as well as battling a resurgent Taliban, whose insurgency has spread out of traditional strongholds in the south and east.

U.S. National Security Adviser Jim Jones said after two days of meetings with Afghan President Hamid Karzai and other political and military leaders in Afghanistan that Washington supported "secure, credible and legitimate elections".