They are robots in the sky and some say they are revolutionizing the way the United States wages wars. Drones are playing a growing role in the US military.

This is one estimate 10,000 unmanned aerial vehicles in the US military's arsenal, in addition to an undisclosed number operated by the CIA - including one that recently killed Abu Yahya al-Libi, al-Qaida's number two leader.

Pakistan objects to the use of drones over its territory. But US Defense Secretary Leon Panetta has given no indication Washington will stop using them against terrorists.

"We made it clear to the Pakistanis that United States of America is going to defend ourselves against those that would attack us, and we have done just that, we have gone after their leadership and we have done it effectively," said Panetta.

Drones are relatively cheap to operate. Their strikes are precise. And they entail no risk to the pilots who operate them from US bases thousands of kilometers away.

At a time of shrinking budgets and growing war fatigue among the American public, the Obama administration has made unmanned aerial vehicles a central component of its new defense strategy.

Michele Flournoy is a former top Pentagon official and an architect of that strategy.

"The whole realm of unmanned systems is going to revolutionize the force over time," said Flournoy. "We are still in the process of understanding what those systems bring in terms of new ways of operating, new ways of working as a military.

By some accounts, that revolution is happening now. UAVs' effectiveness and their small footprint are quickly making them the Obama administration's weapon of choice for US military and intelligence operations.

John Brennan is President Obama's chief counterterrorism adviser:

"It is hard to imagine a tool that can better minimize the risk to civilians than remotely piloted aircraft," Brennan said.

But anti-drone protesters say drones are not risk free and the deaths of bystanders in Pakistan and elsewhere go largely unreported.

Medea Benjamin fears that Americans could become desensitized to war.

"The biggest ethical problem with drones is that it makes killing too easy," said Benjamin.

For US leaders, armed drones have proven their worth and are the way of the future. Activists want a moratorium until laws catch up with the technology in order to keep it in check.

drone: a pilotless aircraft operated by remote control 无人机

moratorium: a suspension of an ongoing or planned activity 中止

Related stories:

Al-Qaida, Taliban rift emerges

Drones: not just for military use

Obama downplays use of US drones in Iraq

美军最新无人侦察机外形酷似男性精子

（来源：VOA 编辑：旭燕）