Gen. David Petraeus, the head of U.S. Central Command, says the American military will face "tough" casualty losses in Afghanistan during the next 12 to 18 months of combat, as the massive western offensive into the southern Afghan town of Marja entered its second week. "They'll be tough. They were tough in Iraq," Petraeus said Sunday on NBC's "Meet the Press." Taliban forces remained formidable, though "a bit disjointed," as NATO-led forces entered a second week of fighting to win control of Marja, said Gen. Petraeus. That assault is the beginning of 12 to 18 months of combat operations designed to eliminate havens for the Taliban and other Islamic militants. About 4,500 of 30,000 additional U.S. troops are on the ground now in Afghanistan in what will be a "hard" effort to gain control of the country, Petraeus said. "I don't use words like 'optimist' or 'pessimist'. I use 'realist.' And the reality is that it's hard but we're there for a very, very important reason and we can't forget that," he said. But Petraeus said that the battle being fought in Marja was the initial salvo in a military campaign that could last 12 to 18 months. The general, who oversees the wars in Afghanistan and Iraq, said that international forces had spent recent months mapping strategy, gathering resources and preparing the leadership of a comprehensive civil-military campaign. We have more of our Special Operations forces going in on the ground, and youve seen the results, he said, with more Afghan shadow governors, the Taliban shadow governors being captured, more of the high-value targets being taken down. The general also reiterated his strong opposition to using torture to gain information from important captives like Mullah Abdul Ghani Baradar, the Talibans top military commander, who was seized recently in Pakistan. Whenever we have, perhaps, taken expedient measures, they have turned around and bitten us in the backside, he said. Whenever Americans have used methods that violate the Geneva Conventions or the standards of the International Committee of the Red Cross, he said: We end up paying a price for it ultimately. Abu Ghraib and other situations like that are non-biodegradable. They dont go away. The enemy continues to beat you with them like a stick. Interrogation methods approved by the Army Field Manual, he said, work well to gain significant information. In his assessment of the campaign against Al Qaeda in the 20 Middle Eastern and Central Asian countries under the purview of the Central Command, he said, Over the course of the last year or so, Al Qaeda has been diminished in that area. With the exception of Yemen, the countries of the Arabian Peninsula, Iraq and Pakistan have continued to make gains. But, having said that, Al Qaeda is a flexible, adaptable it may be barbaric, it may believe in extremist ideology, as it does, but this is a thinking, adaptive enemy, and we must maintain pressure on it everywhere, he said. On the subject of Irans nuclear ambitions, General Petraeus offered an endorsement of the White Houses tactics. Having pursued engagement for a year, he said, the Obama administration has given Iran every opportunity to resolve the issues diplomatically. That puts us on a solid foundation now to go on what is termed the 'pressure track of Security Council sanctions. In keeping with established policy, however, he refused to rule out the possibility of a military strike if Iran continued to defy the United Nations. It is the job of combatant commanders to consider the what-ifs, to be prepared for contingency plans, he said. Im not saying this in a provocative way. Im merely saying that we have responsibilities the American people and our commander in chief and so forth expect us to think those through and to be prepared for the what-ifs.