Bringing Afghan presidential elections forward from August to April as demanded by President Hamid Karzai will not give other candidates time to contest the campaign, an Afghan presidential contender said.

Karzai's call on Saturday for the poll to be held much sooner than almost anyone sees as practically possible was a deft political manoeuvre, analysts say, to force opposition groups to let him stay in office after a May constitutional deadline.

Karzai's decree puts the young Afghan democracy in uncharted constitutional territory and sets the president at odds with the election commission, which set Aug. 20 as the date for polls, and his U.S. backers who supported the commission's decision.

The United States "supports the underlying principles articulated by President Karzai" but still believed August would be a better time to hold elections in a secure environment, State Department spokesman Robert Wood said.

U.S. President Barack Obama has ordered 17,000 more troops to Afghanistan to try to secure the elections in August against the strong threat from Taliban insurgents. Bringing the polls forward would not give the troops time to even arrive in the country.

Other candidates would also be put at a disadvantage, said presidential contender Ashraf Ghani Ahmadzai.

"All candidates and influential figures have been trying to get ready for the campaign in the month of August, but a sudden change to the decision and holding the elections in the month of April will create certain problems," he told Afghan television late on Saturday.

Karzai's decree said the election should be held according to the constitution. That states the president's term ends on May 21 and new polls to elect his successor must be held between 30 and 60 days before that, giving April 21 as the last possible date.

ILLEGITIMATE

Opposition leaders had said Karzai's position would be illegitimate if he remained in office beyond May 21.

The Independent Election Commission (IEC) said a spring election would be impossible because it would have to be organised during the harsh Afghan winter when many areas are inaccessible and people in those areas would be disenfranchised.

"Before deciding the election date, the Independent Election Commission took into account all aspects including funding, security and the wide participation in the polls, and also climate," IEC deputy chief Zekria Barakzai told Reuters.

He said the commission had not yet received an official copy of the decree. "We are waiting to receive the presidential decree and then we will evaluate it and make our decision," he said.

Top of the list of problems for early polls would be the Taliban insurgency raging across much of the south and east up to the fringes of the capital, Kabul. The extra troops Obama ordered deployed in spring were meant to boost security by August.

The Taliban rejected a call from Karzai for them to take part in the election.

"Not only will the Taliban not take part in the election, we also ask the Afghan nation not to participate in it as this is an infidel system and Afghanistan is now a country occupied by foreigners," Taliban spokesman Qari Mohammad Yousuf told the Pakistan-based Afghan Islamic Press.

NATO said it was too early to comment on whether its 56,000-strong force in Afghanistan would be able to secure an election in the next three to seven weeks. Afghan security forces are to take the lead in providing security for the vote.

"It is a fresh presidential decree and we are working on a plan," said Defence Ministry spokesman Zaher Murad.

Ahmadzai, a senior fellow in foreign policy at the Brookings Institution in Washington, also said only the Supreme Court had the right to interpret the constitution.

According to the electoral law, at least 120 days must also be given to organise the polls, meaning there is not enough time to hold them in April.

Hafiz Mansur, the head of one of the two main opposition groups, said his party believed in the constitution but it should not be exploited to "create chaos, disorder and hold the elections unfairly", he told Afghan television.

Ahmadzai called for a large meeting of Afghan political leaders to decide on how best to hold a free and fair election.