More than 50 people were wounded in the Kabul blast, which came despite raised security in for Thursday's election.
 

The Nato-led force said reports indicated some of its troops were among those killed and injured, while the UN said two of its employees were killed.
 

Militants have threatened to disrupt Thursday's vote in which Hamid Karzai is tipped to be re-elected president.
 

However correspondents say he is facing a strong challenge from ex-Foreign Minister Abdullah Abdullah. Several dozen candidates are in the race.
 

In other violence on Tuesday:
 

• A rocket was fired into the presidential compound in Kabul; no-one was reported injured.
 

• Two US soldiers died in a roadside bomb in the east of the country
 

• Two civilians and three Afghan soldiers died when a suicide bomber on foot blew himself up in southern Uruzgan province, police said
 

• In the usually peaceful north, an election candidate was shot dead in Jowzjan province, and three poll workers were killed in Badakhshan when their car hit a bomb
 

I saw wounded people and dead people everywhere   Sawad Kabul shopkeeper   Afghan election fraud is unearthed In pictures: Kabul car bomb

The BBC's Hugh Sykes, in Kabul, says the bombings are likely to make people nervous about going to cast their ballot.
 

The Taliban claimed responsibility for the Kabul suicide blast, which targeted a convoy of foreign troops near a bustling market on the busy Jalalabad road.
 

An Associated Press reporter at the scene saw British soldiers, who were securing the site, collecting what appeared to be body parts from the roof of an Afghan home.
 

Two Afghan UN staff were believed killed in the attack

"I saw wounded people and dead people everywhere," a shopkeeper named Sawad told Reuters news agency.

The explosion sent a huge plume of black smoke into the sky, but Kabul's daily routine was barely affected, says our correspondent.
 

Two Afghan UN staff are believed to have died in the attack.
 

"I am shocked and greatly saddened to have learned that two of my staff members were among those killed in today's suicide bombing," UN special representative Kai Eide said in a statement.
 

The latest violence comes as a BBC investigation found evidence of electoral fraud and corruption ahead of the presidential election.
 

Thousands of voting cards have been up for sale and thousands of dollars have been offered in bribes to buy votes, found the BBC's Ian Pannell.
 

The Afghan Independent Election Commission, which is overseeing the ballot, has been accused of not doing enough to prevent abuses.
 

But a senior commission official, Daud-Ali Najafi, denied to the BBC that voting cards were being sold, saying the cards could only be used be their rightful owners.
 

Thursday's vote will be Afghanistan's second presidential election since the US-led invasion in 2001 toppled the Taliban regime.