Mr Karzai faces a series of challenges from a wide range of candidates
Campaigning has begun in Afghanistan for presidential elections in August.
President Hamid Karzai is seeking another term in office and is facing challenges from 40 other candidates.
Posters promoting the rivals have begun to appear, while vehicles with loudspeakers have been circulating the capital, Kabul, urging people to vote.
The elections - which were postponed from April because of security and logistical problems - come as the US reinforces troops to fight the Taliban.
Supporters of some of the leading presidential candidates are gathering in the capital, Kabul, including those of President Karzai.
He won the first election in 2004 and is the clear front-runner to win these polls as well, even though his reputation has been damaged by his failure to tackle corruption and the worsening conflict with the Taliban.
The BBC's Bilal Sarwary in Kabul says the front runners in the vote are President Karzai, former finance minister Ashraf Ghani, former foreign minister Abdullah Abdullah and former deputy speaker of the lower house of parliament, Mirwais Yasini.
Many of the 44 candidates are not well-known across the country
Our correspondent says that the candidates can broadly be be divided into five groups: those who are only well known in their home communities, those who are better known in the country but have little chance of winning, those who want significant political change and want to alter the country's constitution, those standing on a conservative agenda and those wanting Nato forces to leave the country.
Two women are among the candidates, our correspondent says, in addition to several people who critics say should not be on the list as they do not have the qualifications or profile to stand for office.
Campaigning will last for two months, giving the candidates enough time to travel to the most remote corners of this country. But because of the war, many areas might remain out of bounds.
There are fears that the insurgents could try to attack the polls, so thousands of Nato troops are arriving to reinforce the soldiers already in the country.
The Special Representative of UN Secretary-General for Afghanistan, Kai Eide, appealed to candidates to campaign "with dignity and fairness".
Mr Eide said that "intimidation, inflammatory language and violence of any sort" had no place in the campaign and that it was "critically important" that all candidates conduct their campaign freely and without interference.
"The Afghan people continue to suffer from conflict, hardship and poverty," he said, "however the strength and legitimacy of a future government and provincial authorities depends on the active participation of people in these elections."