A suicide bomber on a motorcycle killed 17 people, including a senior police official and his two bodyguards, in southwest Afghanistan today.
At least 29 people were wounded in the attack in Farah City. Most of the dead and injured were civilians.
The Taliban denied responsibility for the attack.
Violence in Afghanistan has reached its highest levels since the US-led invasion in late 2001. While Taliban militants normally target foreign and Afghan security forces in their attempt to overthrow the government and drive international troops out of the country, most of the casualties are civilians.
Some 1,500 civilians were killed between January and August this year, according to the United Nations.
The latest attack comes a day after President Hamid Karzai was sworn in for his second five-year term in a ceremony attended by dozens of foreign dignitaries.
In his inaugural speech, Mr Karzai said he wanted Afghan forces to take the lead from international military forces in securing the whole country. There are some 110,000 foreign troops, including 68,000 US soldiers, in Afghanistan.
President Barack Obama is due to give a decision in the next few weeks on whether to send up to 40,000 more US troops that his top commander in Afghanistan, Army General Stanley McChrystal, says he needs to quell the strengthening insurgency.
Farah, a mainly desert province along the border with Iran, is one of the areas that has seen a rise in insurgent attacks this year as Taliban militants have spread to the west and north from their traditional bases in the south and east.
The Nato-led force in Afghanistan confirmed the Farah incident, but said no Western troops had been in the area at the time of the attack.