The United States is putting "global stability and international order at risk" by pursuing a policy of targeted extrajudicial drone strikes against suspected terrorists, European politicians have warned.
At least to 3,000 people, including a large number of civilians, are said to have been killed by controversial CIA drone strikes in Pakistan, Somalia and Yemen since 2004.
This week members of the European Parliament said they were "deeply concerned about the legal basis, as well as the moral, ethical and human rights implications" of the drone attacks and urged European Union member states to "contest the US attempt to pervert international law".
In a statement the MEPs said: "We cannot remain silent. The European Union and its Member States must speak up against a practice that will set a dangerous and unwelcome precedent for International Law."
British MEP Baroness Sarah Ludford, the Liberal Democrat European justice and human rights spokeswoman, said on Friday: "US drone killings operate in disregard of the long-established international legal framework about when it is lawful to kill people. This sets an extremely dangerous precedent and risks a destabilising effect on international relations. It could even furnish Al-Qaida with a licence to kill in return."
"European complicity in the ‘War on Terror’ after 9/11, in defiance of legal norms whereby terrorist criminals must be brought to justice through due process, still haunts Europe as well as the US. It is incredible that the US is making renewed and reckless attempts to rewrite the international legal code, and we could get hurt again too."
"Without agreed law the international community cannot hope to justify military action and prevent human rights abuses. As leaders of that community along with the US, the EU and its Member States must boldly state their opposition to this programme, which disregards our common international legal heritage. Silence will be taken as European acquiescence, with potentially disastrous results."
The condemnation came after a briefing in Brussels from United Nations Special Rapporteur for Counter Terrorism and Human Rights, Ben Emmerson QC, who is conducting a UN investigation into the UK and US policy of targeted killings.
Senior British parliamentarians have also raised concerns in Westminster over president Obama's use of drones in Pakistan. Former British Foreign Office minister Baroness Kinnock of Holyhead has warned "action must be taken to ensure that there is accountability and reparations when a drone attack goes wrong".
And Lord West of Spithead, the former head of the Royal Navy and a security minister in the last Labour government, told the House of Lords last month: "War is horrible. Death is horrible. Being involved in the risk is horrible. When one does this remotely from a leafy suburb in your own country and killing people that does make it remote and that does have huge implications and is very worrying and needs a lot of control."
The House of Commons defence committee announced it would conduct an investigation into the British military's use of drones after the RAF decided to expand its use and number of Unmanned Ariel Vehicles.
Pressed by MPs and peers, the UK government has insisted it has only used its own drones inside Afghanistan as the British military's presence there is at the request of the Afghan government. However British intelligence agencies have been accused of passing information to the CIA to help the Americans carry out strikes in Pakistan.
And last month it was reported the UK had a policy of stripping British citizens of their passports on national security grounds - two of who were then killed by US drones.
President Obama's use of drones has recently climbed up the American news agenda following the controversial confirmation of John Brennan as head of the Central Intelligence Agency and Republican senator Rand Paul's thirteen hour senate filibuster against extrajudicial drone killings.
Brennan has previously claimed that no civilians have been killed by drones, based on the Obama administration's decision to designate every military-age male in the target area as a combatant.
On Thursday the White House tried to shut down the debate over whether, as had been initially suggested, Obama had the power to order a drone strike on US soil.
A series of HuffPost/YouGov surveys showed that while a majority of Americans support their use to kill people suspected of being "high-level members of al Qaeda", this is reversed if they are told civilians are at risk of being killed.