* Hopes of brokered ceasefire in 12-year war will spell relief for West
* Kabul explosion coincides with Afghan security handover
* Karzai warns against exploitation of peace talks by "third country" (Adds Taliban said to open office in Qatar)
By Dylan Welch and Hamid Shalizi
KABUL, June 18 (Reuters) - Afghanistan will send a team to Qatar for peace talks with the Taliban, President Hamid Karzai said on Tuesday, as the U.S.-led NATO coalition launched the final phase of the 12-year war with the last round of security transfers to Afghan forces.
Karzai's announcement was the first possible step forward in the peace process, which has struggled to achieve results despite many attempts, and is likely to be applauded by his Western backers.
"Afghanistan's High Peace Council will travel to Qatar to discuss peace talks with the Taliban," Karzai said in Kabul, referring to the council he formed in late 2010.
"We hope that our brothers the Taliban also understand that the process will move to our country soon," Karzai said of the fundamentalist Islamic group that ruled the country with an iron fist from 1996 to 2001.
There was no immediate comment from the Afghan Taliban.
Karzai said three principles had been created to guide the talks - that having begun in Qatar, they must then immediately be moved to Afghanistan, that they bring about an end to violence and that they must not become a tool for a "third country's" exploitation of Afghanistan.
Karzai called on the Taliban last month to fight Afghanistan's enemies in what was widely seen as a swipe against Pakistan days after the neighbours' security forces clashed on their joint border.
There was no immediate comment from Pakistan, which helped the Taliban take power in Afghanistan in the 1990s and is facing a Taliban insurgency itself.
Many Afghan leaders say Pakistan is still helping the militants in Afghanistan, seeing them as a tool to counter the influence of its old rival, India.
An Afghan diplomatic source in Qatar said the Afghan Taliban planned to open an office there as early as Tuesday.
"There is a plan for the office to be open today," said the source. "This will help start the peace talks again."
A team of envoys from the Taliban flew to Qatar in early 2012 to open talks with the U.S. government. But the Taliban suspended the talks in March 2012, saying Washington was giving mixed signals on the nascent Afghan reconciliation process.
An explosion in Kabul on Tuesday that targeted a senior member of the peace council illustrated concerns over how effectively the 352,000-strong Afghan security forces will fight the growing insurgency after most foreign combat troops depart by the end of next year.
Mohammad Mohaqiq, a prominent Hazara politician, escaped unscathed from the attack but three people were killed and 21 wounded, a government official said.
Just a week separated the attack from two large-scale attacks in Kabul claimed by the Taliban, with militants attacking the airport on 10 June, and a suicide bomber killing at least 17 people outside the supreme court the next day.
Karzai was speaking following a ceremony in which the international coalition marked the beginning of its final phase of handover of security to Afghan forces.
Tuesday's attack was 10 km away from and 90 minutes before the handover ceremony attended by about 2,000 people including NATO Secretary-General Anders Fogh Rasmussen, dozens of Western ambassadors and senior Afghan and international officials.
Dubbed "milestone 2013" by NATO, it will culminate in the departure of all NATO troops serving in Afghanistan under the International Security Assistance Force (ISAF) force at the end of next year.
Rasmussen paid tribute to the families of Afghan troops who died defending the country. "They have fought to ensure that international terrorism no longer finds a safe haven in Afghanistan and many have shed their blood for this cause."
Afghan security forces have been rapidly built up by the international coalition, from about 40,000 in 2009 to 352,000 in February this year, comprised of 195,000 Afghan army soldiers and 157,000 police.
The transfer of security responsibility began in July 2011, with a handover by ISAF of the country's most peaceful province, Bamiyan.
There have been three further rounds since, taking to 87 percent by last December the proportion of the Afghan population protected by the Afghan state.
Tuesday's tranche comprises restive eastern and southeastern provinces bordering Pakistan. These include Helmand, Kandahar, Paktika, Paktia, Khost, Nangarhar, Kunar, Laghman, Logar and Nuristan.
Fatalities among the Afghan security forces show how soon they have been expected to take the burden of the Afghan war.
In one year, the Afghan state has lost more troops than NATO has across the entire war.
(Addiitional reporting by Mirwais Harooni in Kabul and Amena Bakr in Dubai; Editing by Clarence Fernandez and Nick Macfie)
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