Shortly before departing for a crucial London conference on the war-wracked country's future, Ban told reporters that de Mistura, a 63-year-old veteran UN
troubleshooter, would take up his new post on March 1st. De Mistura succeeds Kai Eide of Norway, who has been criticized over his handling of Afghanistan's fraud-marred election in August.
Ban said the Swede "brings an enormous wealth of experience and skills" to the post, but also took care to praise Eide "for his leadership of UNAMA (the UN mission in Afghanistan) during a very difficult period."
De Mistura has been deputy executive director for external relations of the
Rome-based World Food Program since last July, when he stepped down as UN special envoy to Iraq after less than two years in the post.
For nearly four decades, he has served the world body in conflict-ridden hot spots such as Somalia, the Middle East, the Balkans and Nepal.
Ban also noted that Thursday's London conference on Afghanistan "comes at a critical moment."
"The Afghan people want a larger say in their future especially in terms of development and national ownership is essential," he said. "At the same time, Afghans need to know that the international community will support them over the long term in building their institutions of government."
He stressed the need for "a more balanced approach" by the international community, giving as much importance to meeting the needs of Afghan civilians in terms of development as to the need to combat the Taliban insurgency.
The London conference, which brings together some 70 countries and organizations, is expected to agree that Afghanistan must assume responsibility for its own security as rapidly as possible, according to the organizers.
This will require the training of more Afghan police and soldiers to take over from the international forces, which number about 110,000 troops due to swell to 150,000 this year.
Karzai is expected to ask the conference to fund a $500 million programme to reintegrate Taliban fighters by offering them jobs and security to stop fighting, a move that could prelude peace talks.
The Islamist movement has repeatedly rebuffed negotiations with Karzai and his Western backers, and in an emailed statement Wednesday reiterated a call for all foreign troops to leave the country.
The only solution to the conflict was for all "invading forces" to leave immediately, the statement said.
On Tuesday, Karzai won regional support in Istanbul for his efforts to cajole Islamist insurgents to lay down their arms, as Germany offered more troops and cash for the ravaged nation.
After talks with his Turkish and Pakistani peers, as well as officials from countries such as China, Iran and Russia, Karzai said moderate Taliban fighters should be brought back into the fold.
In a joint statement after the meeting in Istanbul, the participants declared that they "support the Afghan national process of reconciliation and reintegration... in a way that is Afghan-led and -driven."
Meanwhile Ban also talked about his attendance at the African Union summit in Addis Ababa this weekend.
He said he would discuss with African leaders three key issues:
*development, particularly the need to help African countries meet the poverty-reduction Millenium Development Goals
*climate change and its "potentially devastating impact on Africa, as well as the important role African leaders can play in supporting the December Copenhagen accord
*regional conflicts and upcoming elections