* Afghan president picks Tajik VP ahead of polls
* Candidate considered close to opposition leader Abdullah Abdullah
* At least 15 dead in bombing weeks before crucial election (Releads with VP choice)
By Mirwais Harooni and Hamid Shalizi
KABUL, March 18 (Reuters) - Afghan President Hamid Karzai nominated a new vice president on Tuesday, a moderate politician from the same ethnic group as an opposition candidate contesting next month's presidential election.
Mohammad Younus Qanuni replaces Marshal Mohammad Fahim Qasim, who died following an illness last week. Both men are Tajiks, Afghanistan's second largest ethnic group.
Many Tajiks fought fiercely against the Taliban in the run-up to the U.S. invasion in 2001. They are an important constituency in presidential polls scheduled for April 5, which should mark the first time in Afghanistan's history that one elected government has handed power to another.
Karzai has not officially backed any of the nine candidates currently campaigning, but his two brothers have endorsed former Foreign Minister Zalmay Rassoul, cementing the official's reputation as a palace favourite.
The other two front-runners are Abdullah Abdullah, an eye surgeon and senior aide to a slain anti-Taliban Tajik militia leader, and Ashraf Ghani, a former World Bank official who has teamed up with another militia leader blamed for human rights abuses.
Some will see Qanuni's appointment as an attempt to keep Tajik votes on Rassoul's side. But others argue the president is simply maintaining an ethnic balance in the government and say Qanuni has publicly supported Abdullah in the past.
All the presidential candidates are Pashtun, Afghanistan's largest ethnic group, except for Abdullah, whose mother is Tajik and whose father is Pashtun.
Qanuni's appointment still has to be confirmed by legislators but it is unlikely to face serious opposition.
BOMBING KILLS 15
In a separate incident, a suicide bomber killed 15 people in an attack on a busy marketplace in northern Afghanistan on Tuesday, officials said.
The Taliban have threatened to kill anyone who takes part in the elections, and eight people involved in political campaigning have been killed since electioneering started last month. A group of election officials has also been kidnapped. It was not clear if the bombing was related to the election.
At least 47 people were wounded when the suicide bomber driving a three-wheel rickshaw blew himself up in Maimana, the provincial capital of Faryab province, the Health Ministry said in a statement.
"It was a bazaar day and everybody was busy buying or selling when the bomber detonated his explosives," Faryab governor Mohammadullah Batash told Reuters.
Two children were among the dead, the United Nations said.
Nicholas Haysom, the top United Nations official in Afghanistan, said such bombings could be a war crime.
"Their use in a distinctly civilian location such as a market is atrocious and cannot be justified," he said in a statement.
The United Nations said such bombs - called improvised explosive devices - have killed 190 civilians in Afghanistan so far this year, a 14 percent increase from the same period last year. (Reporting by Mirwais Harooni and Katharine Houreld in Kabul Bashir Ansari in Mazar-e-Sharif; Writing by Jessica Donati, Editing by Maria Golovnina)