The use of unmanned aerial vehicles (UAVs), or drones, is expected to increase in the future, the military aerospace expert for the International Institute for Strategic Studies (IISS), Doug Barrie, said on Wednesday.

According to the IISS' annual Military Balance report, as drone usage increases, the legal and ethical questions they raise come to the fore. One key issue is whether attacks on people can be justified as self-defense.

The report said that lethal strikes will be carried out by humans piloting the drones because handing that power over to a machine "will remain a threshold legislatures and the public will likely be unwilling to cross."

While drones have been almost exclusively a tool used by Western militaries, smaller and cheaper technology has opened up the market to private companies and emerging economies.

Barrie said that greater drone usage will also lead to greater variability.

"We're going to see more of these things," he said. "They will proliferate from the kind of system you can stick in your backpack to full-blown combat strike."

China leads Asia expansion

The report said that China's increased military power has prompted neighboring Asian countries to boost their defense budgets. While the US ($600 billion) spends nearly six times more than China ($112 billion) on its armed forces, those two could be even by 2030.

However despite an influx of cash, China's military capabilities and ability to project power will take several more years to catch up with the US.

China, Japan and South Korea were responsible for more than half of East Asia's military jump in spending, which increased 11.6 percent from 2010 to 2013.

"These outlays are fueling heightened military procurement in a region replete with conflicting territorial claims as well as long-standing potential flashpoints," said IISS director-general John Chipman. "Not least because of the Asia-Pacific's central place in the global economy, the rapid pace of capability development and the potential for accidental conflict and escalation will continue to be of concern."

While Asia saw an increase in defense spending, Europe saw a decrease of 2.5 percent.

Following the US and China, Russia ($68.2 billion) and Saudi Arabia ($59.6 billion) were third and fourth respectively on the list of biggest military spenders. Germany was eighth on the list with a budget of $44.2 billion, ahead of India ($36.3 billion).

Afghanistan topped the list of defense budget as a share of gross domestic product with 13.8 percent, followed by Oman (11.7 percent), Saudia Arabia (8 percent) and Iraq (7.2 percent).

dr/lw (AFP, dpa)