KABUL (Reuters) - NATO's secretary-general said on Wednesday 4,000 more soldiers were needed to secure Afghanistan's presidential election in August and to make sure the vote was credible and fair.

Violence is at its highest level in Afghanistan since the U.S.-led invasion in late 2001 toppled the Taliban. Around 5,000 people, including more than 2,000 civilians, were killed in fighting last year alone, the United Nations has said.

NATO chief Jaap de Hoop Scheffer said he wanted four more battalions in place for the August 20 election. A NATO battalion is just under 1,000 troops. There are around 70,000 foreign soldiers now in Afghanistan.

The election is seen as the key test of progress in Afghanistan and the success or failure of the polls, diplomats say, will override any other events this year.

The United States will send an additional 17,000 soldiers to the country over the next year and NATO commanders have also demanded member states send temporary deployments to secure the election but had not previously given numbers.

Resurgent Taliban militants have managed to extend the size and scope of their attacks in recent years, prompting a stalemate and discouraging some NATO contributors from sending soldiers in areas where militants are most active.

Germany, the third largest troop contributing nation in Afghanistan with around 3,500 soldiers, has already committed an extra 600 troops for the election.

At an earlier news conference with Afghan President Hamid Karzai, de Hoop Scheffer said 2009 would be vital for Afghanistan and emphasized the importance of holding a fair election.

Of course, these elections in a certain way ... will be a challenge, but we are there to meet this challenge, the NATO chief said.

Every Afghan citizen should have the right where he or she lives, to go to the polls. If you say free, fair and credible, free means of course, free to vote for whoever you would like to vote for.

According to the constitution, the election is to be held in spring but the date was postponed until August due to the Afghan winter and to give foreign troops enough time to ensure security.

Karzai's term is meant to end on May 21, in line with the constitution, although he has yet to officially announce his plans for candidacy. He has led Afghanistan since the Taliban's ouster and won elections in 2004.

Afghanistan had achieved a lot under his leadership, Karzai said, adding much more needed to be done, including reconciliation with Taliban-led insurgents.

Karzai said he hoped to bring over those insurgents who were not allied with al Qaeda, but he did not elaborate on the process or who was involved from the government or the Taliban.

U.S. President Barack Obama said recently he was open to the idea of talks with moderate Taliban but the austere Islamic movement, overthrown after the September 11 attacks for sheltering al Qaeda leaders, has shunned Obama's call and said they would continue to fight to drive out foreign forces.

(Editing by Golnar Motevalli and Dean Yates)

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