Washington (dpa) - US President Barack Obama praised the elections that took place in Afghanistan on Thursday as successful despite violence that claimed the lives of 26 people.

"We had what appears to be a successful election in Afghanistan, despite the Taliban's efforts to disrupt it," Obama said in a radio interview.

Afghans flocked to the polls on Thursday, braving Taliban threats and a series of attacks that left 17 security forces and 9 civilians dead. Twenty insurgents also died.

Turnout and vote results are not expected for days. Incumbent President Hamid Karzai must secure 50 per cent of the vote against his two main rivals, former foreign minister Abdullah Abdullah and former finance minister Ashraf Ghani, to avoid a runoff.

US Marines launched a major assault in Helmand province in recent weeks to push out the Taliban and improve security for the country's first independently conducted presidential and provincial elections in decades.

The United States views the election as a key step toward assessing stability in the country as it intensified the fight against al-Qaeda and the Taliban.

More US soldiers died in Afghanistan in July than in any other month since the US-led assault to oust the Taliban began in October 2001.

"We are going to keep on putting pressure on" the Taliban and al- Qaeda, Obama said. "We've got to make sure that we are really focused on finishing the job in Afghanistan, but it's going to take some time."