This past week when President Barack Obama nominated John Brennan to run the Central Intelligence Agency (CIA), there were mixed reviews by European commentators.

The Guardian, the left-wing British daily newspaper, suggested that Brennan, a veteran CIA operator, would “shore up a new paramilitary role for the nation’s intelligence services.”

The Economist magazine took a different line. It reported that Brennan, as Obama’s advisor for Homeland Security and Counterterrorism, “has been increasingly open about the legal and ethical context” of using the drones, the unmanned aerial vehicles.

Germany’s left-wing Frankfurter Rundschau went further. It argued that Brennan was no gung-ho anti-terrorist fighter. This was a man, the paper said, who spent much time pondering the moral, political, and legal implications of using drones to kill suspected terrorists.

Indeed, Brennan himself has insisted that the United States “wanted to use the drones responsibly.” In a major speech at the Woodrow Wilson Center, he added that Obama wanted “drone warfare” to be brought under the control of the armed forces, who are accountable and subject to a strict chain of military command, instead of remaining under the secretive CIA intelligence agency.

Given Brennan’s views on such a controversial issue, this would be a good time for Europe to consider using his nomination as CIA chief to forge a transatlantic consensus over how to apply the laws of war to targeted killings carried out by drones.

The laws of war permit attacks against military objectives that include enemy fighters, weapons, or ammunition, according to Human Rights Watch legal experts. International human rights law also allows the use of lethal force outside of armed conflicts if it is strictly and directly necessary to save human lives.

But how does the law apply to unmanned aerial vehicles? There is in fact little difference between using drones and other weapon systems in warfare. So far, both are employed under a chain of command, even if transparency is often minimal. But what will happen once there are fully automated drones which can be programmed to decide when and where to attack? Who will be responsible for the chain of command? Who will be held accountable when civilians are killed?

Democratic governments have dodged these issues, justifying secrecy with security reasons. That has been a common CIA response too.

But the more democratic governments and their intelligence agencies take refuge in secrecy, the more civil rights organizations suspect them of concealing the truth over the use of targeted killings and the number of civilian casualties they cause.

In the United States, civil liberties movements constantly challenge the military use of drones. But their usage is still widely accepted by the public.

In Europe, the public strongly opposes Obama’s drone wars— even though, unofficially, some leaders are relieved that the United States has eliminated leading Al Qaeda operatives, including Osama bin Laden.

But Europeans are not innocent when it comes to the use of drones. Britain, France, and Germany are just three of several European countries that have used surveillance drones in NATO’s mission in Afghanistan. Britain has also employed armed drones there.

And the use of drones by European countries is increasing.

Last year, NATO agreed to buy U.S. drones worth over one billion euro. They will be used to counter attacks by improvised explosive devices in Afghanistan and to protect humanitarian operations and disaster relief missions. The drones’ main base will be at Sigonella in Italy. The 28 Allies will carry the costs of setting up and running the base and its subsidiaries.

What is not clear are the rules under which NATO will use them.

The EU has to address the lack of such rules, too.

Last November, Frontex, the EU’s border control system, said it would use drones to protect Europe’s external borders from illegal immigrants. The rules are not clear.

France is considering using drones in northern Mali that is now controlled by radical Islamists. Paris is moving two surveillance drones to western Africa from Afghanistan as the EU prepares to send a military training mission to Mali.

The United Nations wants to use drones as well. Its peacekeeping chief, Hervé Ladsous this week asked the Security Council to support the deployment of drones to support the 17,700 U.N. peacekeepers and over 1,400 international police in Congo. The drones, he claimed, would help peacekeepers track armed groups, help protect civilians and themselves from ambushes.

Employing surveillance drones is only the first step, though, and much less controversial than the use of armed drones.

In Asia, China and Japan are locked in a dangerous standoff over the disputed islands in the East China Sea. Both countries are developing or acquiring armed drones to help assert their claims over the islands.

Drones are becoming an essential part of modern warfare and civilian use. But international law has to be updated to take into account the use of this new technology.

Precisely because they are becoming crucial to protecting troops and lives, identifying terrorist movements and pinpointing danger zones after catastrophes, it is time European governments agreed clear and transparent rules for their use.

With Brennan at the helm of the CIA, there could be an opportunity for both sides of the Atlantic to establish an international code of conduct for the use of drones. It is an ambition worth pursuing.