* Negotiators launch final efforts to sign a peace deal
* U.S. peace envoy says 'ready for a good agreement'
* Uncertainty around the deal triggers anxiety among Afghans
* At least 1,500 civilians killed and injured in July:UN (Adds Taliban, civilian quotes, details)
By Rupam Jain
KABUL, Aug 3 (Reuters) - A fresh round of U.S.-Taliban peace talks began in Qatar's capital Doha on Saturday, officials said, describing it to be the "most crucial" phase of negotiations to end the 18-year war in Afghanistan.
Senior officials privy to the talks said a peace agreement could be expected at the end of the eighth round of talks, possibly before Aug. 13, and would enable foreign forces to be withdrawn from the war-torn country.
Zalmay Khalilzad, the U.S. peace envoy for Afghanistan who has held a series of meetings with Taliban leaders since last year, reached Doha on Friday night.
"Just got to Doha to resume talks with the Taliban. We are pursuing a peace agreement not a withdrawal agreement," Khalilzad wrote on Twitter.
"A peace agreement that enables withdrawal. Our (U.S.) presence in Afghanistan is conditions-based, and any withdrawal will be conditions-based," he said, adding the Taliban are signaling they would conclude an agreement.
"We are ready for a good agreement."
Two sources with knowledge of the talks said an agreement on the withdrawal of foreign forces in exchange for security guarantees by the Taliban is expected before Aug.13
About 20,000 foreign troops, most of them American, are now in Afghanistan as part of a U.S.-led NATO mission to train, assist and advise Afghan forces.
The hardline Islamist Taliban group now controls more territory than at any point since the United States bombed them out of power in 2001.
Two Taliban spokesman Suhail Shaheen and Zabihullah Mujahid said a 19-member Taliban negotiation team will represent them in the Doha peace talks.
"The issue of forces withdrawal has prolonged the peace talks and delayed the deal," said a senior Taliban commander based in Afghanistan on conditions of anonymity.
"There was no way we would allow permanent stay of U.S. forces in Afghanistan after signing a peace deal with them," he said, adding that Taliban will provide complete assurance that no foreign militant group will be allowed to use Afghanistan to launch attacks against the United States and its allies.
Leaders of the insurgent group have repeatedly stated that a ceasefire or talks with the Afghan government and civil society members will not take place until the United States announces a plan for foreign force withdrawal from Afghanistan.