Partial Afghan election returns show President Hamid Karzai has extended his lead in last week's vote, but is still falling short of the 50% needed to avoid a run-off.

With results from about a third of polling stations tallied, Mr Karzai leads his main rival, former foreign minister Abdullah Abdullah by 46.3% to 31.3%.

The latest results extend Mr Karzai's lead substantially from earlier partial figures, but they still suggest he would face a run-off scheduled for early October.

Results have been coming in at different rates from different provinces, so it is difficult to guess at the final outcome.

Votes could also be thrown out by a complaints watchdog which says it is probing more than 2,000 accusations of fraud and abuse, including 270 serious enough to alter the outcome.

Meanwhile, British Prime Minister Gordon Brown made an unannounced visit to southern Helmand province today, saying he wanted more Afghan troops to share the burden of fighting the Taliban.

Mr Brown has been under fire back home from retired commanders and critics who say he has failed to send enough troops or equipment to keep British forces safe.