A suicide bomber killed at least 16 people at a crowded market in northern Afghanistan on Tuesday, officials said, despite a tightening of security for presidential elections less than three weeks away.
The Taliban have vowed to disrupt the upcoming presidential elections in Afghanistan and called for attacks on officials, politicians and campaigners
There was no immediate claim of responsibility for the attack in Maimanah city, the capital of remote Faryab province which borders Turkmenistan and has a mixed population of Uzbek, Turkmen and Pashtun ethnic groups.
A week ago Taliban insurgent leaders vowed to target the presidential election, urging their fighters to attack polling staff, voters and security forces before the April 5 vote to choose a successor to Hamid Karzai.
"It was a suicide bombing in the middle of Maimanah city during the Tuesday bazaar," provincial governor Mohammadullah Batash told AFP.
"The blast happened on the main roundabout, which was very crowded. The bomber used a three-wheeler packed with explosives."
Abdul Ali Haleem, the provincial health director, said 16 people had died and 40 were treated for injuries, among them a pregnant woman and two children aged six and seven.
Northern Afghanistan is generally more peaceful than the south and east but Islamist insurgents, rival militias and criminal gangs are active in some districts.
Six Afghan employees of the aid group ACTED working on rural development projects were shot dead in Faryab in December by suspected Taliban gunmen.
- Rising poll violence -
The United Nations envoy to Kabul warned on Monday that election-related violence was on the rise in Afghanistan, where NATO combat troops are withdrawing after 13 years of fighting a fierce Islamist insurgency.
"Security will have a major impact on these polls," Jan Kubis said in an address to the UN Security Council in New York, adding he was "gravely disturbed" by the Taliban threat to unleash "a campaign of terror".
Previous Afghan elections have been badly marred by violence, with 31 civilians and 26 soldiers and police killed on polling day alone in 2009 as the Islamist militants demonstrated their opposition to the US-backed polls.
Another bloodstained election would damage claims by international donors that the hugely expensive military and civilian intervention since 2001 has made progress in establishing a functioning state system.
Karzai, who is barred from serving a third term in office, has consistently said Afghanistan will hold a safe and clean election, despite previous violence and allegations of massive fraud when he won the last poll five years ago.
"We should try our best for a transparent, free and secure election," he told parliament on Saturday.
On Tuesday he condemned the Faryab bombing as a "terrorist attack" plotted by foreigners.
The election front-runners are Abdullah Abdullah, who came second in 2009, former foreign minister Zalmai Rassoul and former World Bank economist Ashraf Ghani.
Unidentified men shot dead two of Abdullah's aides in the western city of Herat in early February.
The next president will face a testing new era as the Afghan army and police take on the Taliban without the assistance of 53,000 NATO combat troops.
Karzai on Tuesday nominated Yunus Qanooni to replace Vice-President Marshal Mohammad Qasim Fahim, who died 10 days ago of natural causes.
Qanooni, like the late Fahim, is an ethnic Tajik, and he may play a key role in deal-making after the election results.
Rassoul and Ghani are seen as competing for the Pashtun vote, which is the largest ethnic bloc, while Abdullah draws widespread Tajik support.