Gates said the Army would grow to 569,000 soldiers from the current 547,000 and comes as the US military shifts its focus from the war in Iraq to a growing Taliban insurgency in Afghanistan.

"This is an important and necessary step to ensure that we continue to properly support the needs of our commanders in the field while providing relief for our current force and their families," Gates told reporters at the Pentagon.

"The Army faces a period where its ability to deploy combat units at acceptable fill rates is at risk," he said.

The initial expansion cost is estimated at $1.1 billion through fiscal year 2010, which begins on Oct. 1. The Pentagon is expected to absorb those costs although more funds approved by Congress could be necessary in the second and third years of the expansion.

Mounting violence

The boost to troop numbers was recommended by the Army's civilian and military leadership and has been strongly endorsed by US President Barack Obama, who has ramped up the US effort in Afghanistan in the face of mounting violence there. He has ordered the deployment of 21,000 more troops to the war-torn country.

However, the Pentagon said the temporary Army growth does not necessarily mean the US would be sending even more troops to Afghanistan on top of those Obama has ordered.

The US commander in Afghanistan, General Stanley McChrystal, will give an assessment of the situation there to the Pentagon next month. He has indicated he would be willing to ask for more troops if he saw the need, despite political and economic considerations.

There are currently about 58,000 US troops in Afghanistan and 130,000 in Iraq.

Military leaders have expressed concern recently over the stress on the US military, especially given the rising number of suicides among American servicemen and women. Last year, the suicide rate in the military surpassed the rate in the civilian population. In 2008, 128 soldiers took their lives, up from 115 in 2007.

The temporary troop increase will help expand "dwell time," the period that soldiers spend at home between deployments. Longer dwell time is considered vital to maintaining the morale of service members.

NATO warning

In London, NATO Secretary-General Jaap de Hoop-Scheffer warned that terrorism would spread through the world if NATO forces fail in Afghanistan. Speaking to foreign policy experts, he said failure in Afghanistan would give al-Qaida "a free run again, and their terrorist ambitions are global."

He urged NATO allies to do more in Afghanistan and has shared US frustration that many nations deployed as part of the NATO-led International Security Assistance Force (ISAF) in Afghanistan will not take part in combat missions because of opt-outs they have secured.

German troops, for example, are mostly involved in the training of Afghan security forces, avoiding active combat missions such as the operation currently being led by US and British forces against the Taliban in the south.

"The true test of our alliance, therefore, lies in its ability to convince allies to show the necessary solidarity and to increase their willingness to share burdens equitably."

Solana in Kabul

On Tuesday, EU foreign policy chief Javier Solana is in Afghanistan for talks with President Hamid Karzai and some of the rivals running against him in elections to be held on August 20.

Solana meets the Afghan foreign minister, Rangin Dadfar Spanta, as well as the head of the EU election observation mission in the country. The EU has already sent 16 election observers and some 100 are expected to be on the ground on election day.

The visit comes as troop casualties are climbing in the face of an increasingly violent campaign by Taliban militants. Growing casualty numbers have hurting public support levels for the Afghan mission in several countries, including Germany.

jam/Reuters/AP/AFP

Editor: Neil King