Kabul ? President Hamid Karzai widened his lead over his main challenger in election returns released Saturday, creeping toward the 50 percent mark that would enable him to avoid a run-off in the divisive presidential contest.

Karzai’s top challenger Abdullah Abdullah stepped up his fraud charges, raising doubts whether the former foreign minister’s followers would accept the incumbent if he wins in the first round.

Accusations of fraud in the Aug. 20 vote have poured into the Electoral Complaint Commission, which must investigate the allegations before final results can be announced.

Fraud allegations from Abdullah and other presidential candidates as well as low turnout in the violent south could strip the election of legitimacy, not only among Afghans but also among the United States and its international partners that have staked their Afghan policies on support for a credible government.

A widely accepted Afghan government is one of the pillars of President Barack Obama’s strategy to turn the tide of the Taliban insurgency. The election controversy has boiled over at a time of rising U.S. and NATO casualties, undermining support for the war in the U.S., Britain and other countries with troops here.

British Prime Minister Gordon Brown paid a surprise visit Saturday to British troops in southern Afghanistan’s Helmand province, hoping to counter critics who accuse his government of failing to support Britain’s mission here. A British Marine was killed by a bomb in Helmand on the day of the prime minister’s visit, the Ministry of Defense said in London.

Figures released Saturday show Karzai with 46.2 percent of the votes against Abdullah’s 31.4 percent. The results are based on 35 percent of the country’s polling stations, meaning the percentages could still change dramatically.

Few results have been announced from northern Balkh province, where Abdullah was expected to run strong, and from some southern Pashto-speaking provinces where Karzai draws his support.

Karzai’s aides appeared confident that the president would score a first-round victory and avoid a run-off, which would probably be held in October if needed.

By contrast, Abdullah has been stepping up his charges, telling Italy’s RAI television that Karzai was responsible for “state-crafted, massive election fraud.”