WASHINGTON As US-led coalition forces in Afghanistan come under increasing pressure, Defence Secretary Robert Gates says progress is being made there and defended their strategy despite a new UN report that found security is deteriorating. Gates, speaking on Fox News Sunday, amid growing level of pessimism over US operations in Afghanistan, said the spike in American casualties was expected and that people are too quick to say the war is going badly. A UN report released Saturday found that roadside bombings and assassinations have soared the first four months of the year amid ramped up military operations in the Taliban-dominated south. The report, which Secretary-General Ban Ki-moon submitted to the UN Security Council this week, said Afghanistans overall security situation has not improved since his last report in March. But the report appeared to conflict with Gates assertions, including his assessment that the Afghan army is becoming increasingly ready to assume responsibility of the country. Separately, Gates expressed optimism that the new UN sanctions imposed on Iran, when coupled with other actions taken by the US and European states as well as internal divisions within Irans government, will weaken Tehran. Responding to questions about progress in Afghanistan, Gates said the war is a tough pull, but he said momentum is shifting toward the United States and its partners. He acknowledges that the war effort in the Taliban heartland of southern Afghanistan is going more slowly than planned. He also acknowledged problems with corruption and thievery among the Afghan army forces, who are supposed to take over when the United States and other countries leave Afghanistan. The Obama administration on Sunday reaffirmed its pledge to begin pulling U.S. troops out of Afghanistan next summer. But the Pentagon and the White House still are saying different things about how many troops will leave - and when. White House Chief of Staff Rahm Emanuel told ABCs This Week that the July 2011 date to begin withdrawal is firm. Emanuel didnt dispute quoted remarks by Vice President Joseph Biden that a whole lot of troops would leave. Gen David Petraeus, who oversees the Iraq and Afghanistan wars, told Congress last week that he had recommend putting off the withdrawal if need be. He said security conditions and the Afghan government have to be ready to handle a U.S. drawdown.