The Pentagon on Sunday opposed setting timetable to withdraw U.S. troops from Afghanistan as U.S. President Barack Obama is weighing on a decision whether to further increase troop levels there.

U.S. Secretary of Defense Robert Gates told CNN during an interview that setting such timelines or laying out an exit strategy would be a "strategic mistake" that could embolden al-Qaida and the Taliban.

"The reality is, failure in Afghanistan would be a huge setback for the United States," he said, suggesting that a premature pullout would be perceived by the extremists as a victory over the United States, similar to the former Soviet Union's withdrawal from the country in 1989.

"Taliban and al-Qaida, as far as they're concerned, defeated one superpower. For them to be seen to defeat a second, I think, would have catastrophic consequences in terms of energizing the extremist movement, al-Qaida recruitment, operations, fundraising, and so on," Gates said.

The Obama administration is rethinking its strategy in Afghanistan in the wake of its election last month.

The Pentagon, as a result, has delayed issuing a request by Stanley McChrystal, the top U.S. and NATO commander in Afghanistan, for additional troops.

Some Democratic lawmakers opposed escalating the war.

Democratic senators Russ Feingold and Dianne Feinstein called for setting a timeline to withdraw troops.

According to plans which Obama have already announced earlier this year, U.S. troop levels in Afghanistan will grow to 68,000 later this year.

However, many military commanders and analysts argued that number is still too small to achieve U.S. objectives.

Obama said that he won't decide whether to send more troops until he has "absolute clarity about what the strategy is going to be."

(Xinhua News Agency September 28, 2009)