WASHINGTON - Afghan President Hamid Karzais challenger called for a dramatic increase in US troops to ensure security in Afghanistan, suggesting a failure to send in reinforcements could put his country at risk of falling to insurgents. The need for more troops is there in order to reverse the situation, Abdullah Abdullah, who will face off against Karzai in a run-off election in two weeks, told Fox News Sunday. President Obama is deliberating over a request from his top commander for such an increase. Hes weighing a call by Gen Stanley McChrystal and other military officials for 40,000 more troops against calls to pursue a more surgical strategy aimed at top Al-Qaeda leaders, particularly in Pakistan. But Abdullah did not say whether Obama is taking too long to determine whether to grant his top commanders request for more forces. Even if the decision is made today it doesnt mean tomorrow well have troops on the ground. It will take time, he said. But he suggested that as long as Karzai is in power, the war effort will be hampered. The Afghan side has not been able to deliver, and the Afghan side has been led by Karzai, Abdullah said. A run-off was ordered following findings of widespread fraud in the August election, much of which tilted in Karzais favour. In a separate interview with CNN, former Afghan foreign minister Abdullah said he would rather be in Opposition than a power-sharing arrangement with Hamid Karzai. Abdullah said he would accept Karzais re-election if the process is transparent and credible. My trust in becoming a candidate was not to be part of the same government, part of the same deteriorating situation, he said. Mine was for a change in this country. Mine was for bringing hopes for the people of this country and making the people of Afghanistan true participants in their politics, in the governance, in the developmental process, in the security situation and as a whole.