The Secretary-General is making a two-day visit while NATO forces are engaged in a massive counter-insurgency operation in the Taleban's primary stronghold in southern Afghanistan.
Speaking to reporters in the Afghan capital Wednesday, the NATO chief, Jaap de Hoop Scheffer, said that despite stiff resistance, NATO forces will prevail.
Almost exactly five years after the September 11 terrorist attacks on the United States, he says any failure in Afghanistan would be felt around the world.
"As we speak, NATO forces in southern Afghanistan are fighting, side by side with the Afghan National Army. Why are they fighting? Because they and we and you do not want the terrorists to win," he said.
NATO assumed command in the south on July 31.
"Operation Medusa" was launched Saturday in the southern province of Kandahar. NATO officials say the offensive has already killed more than 250 militants and soldiers have cornered at least 600 suspected Taleban insurgents as operations continue.
This has been Afghanistan's bloodiest year since U.S. forces ousted the Taleban regime in 2001 for harboring al Qaida leader Osama bin Laden.
Fighting throughout the country has surged dramatically since January, including a number of suicide bomb attacks inside the previously secure capital.
De Hoop Scheffer told reporters that significant challenges obviously still remain for Afghanistan, not all of which can necessarily be solved militarily.
"And if I say there is no military solution for this nation in the long term it is because there is no security - no lasting security - without development," continued De Hoop Scheffer. "Development has to take place and development means fighting corruption, means finding a solution for the scourge of narcotics [and] means reforming the legal and judicial system."
According to the United Nations, Afghanistan's unemployment rate is around 40 percent A new U.N. survey says the country's illegal opium crop is expected to reach record levels this year.
De Hoop Scheffer and Afghan president Hamid Karzai signed an accord providing more international support for local security and development programs.
President Karzai is also scheduled to meet with Pakistan President General Pervez Musharraf.
Afghan officials accuse Islamabad of not doing enough to stop Taleban insurgents from establishing bases in Pakistan and launching cross-border raids.