KABUL (AFP) US Defense Secretary Robert Gates, wrapping up a final visit to Afghanistan as Pentagon chief, said Tuesday that US-led forces are on the verge of securing a "decisive blow" against the Taliban. "I leave Afghanistan today with the belief that if we keep this momentum up we will deliver a decisive blow to the enemy and turn the corner on this conflict," Gates told coalition officers in Kabul. "And if we do, it will be because of the service and sacrifice of all of you," he said, before departing for Brussels. During a four-day trip that took him to American bases in the south and east, Gates offered a cautiously optimistic forecast for the war effort, saying now was not the time to ease up on the Taliban-led insurgency. Although the main purpose of his trip was to say goodbye to troops, Gates found himself sparring at a distance with White House aides who are pushing for a faster drawdown of the 100,000-strong US force. Gates' farewell remarks reflected his view that a troop surge in the nine-year war has begun to bear fruit and that a withdrawal, set to start in July, should proceed at a cautious pace. His comments in recent days amounted to a rebuttal to some White House officials who believe the death of Osama bin Laden and a ballooning budget deficit demand a steep reduction in the US military presence in Afghanistan. Appointed by former president George W. Bush in December 2006, Gates has spent his time at the Pentagon consumed with the wars in Afghanistan and Iraq. In Brussels, Gates is due to attend a meeting of NATO defence ministers on Wednesday and Thursday, where the drawdown in Afghanistan and the alliance air campaign in Libya will top the agenda. Meanwhile, US Defense Secretary Robert Gates is locking horns with White House aides over Afghan troop numbers as he nears the end of his tenure, with the debate over war strategy playing out in the media. The run-up to a decision by President Barack Obama this month on a US troop drawdown has once again exposed fissures between military leaders and White House officials over the war, which first came to prominence during a strategy review in 2009. As Gates bid an emotional goodbye to US troops in Afghanistan before he leaves office this month, he offered a rebuttal to those who argue the death of Osama bin Laden and a worrisome budget deficit require a major reduction in the 100,000-strong US force in Afghanistan. "We've still got a ways to go," Gates said of the war effort. "I think we shouldn't let up on the gas too much, at least for the next few months," he told troops Monday at a base in the eastern province of Ghazni.