The use of armed drones have practical and moral consequences for conflict and warfare – and the government needs to take action to address them, the U.S. Catholic bishops have said.

"It is incumbent on a nation's leaders to recognize that the use of drones can lower the threshold on conflict and take appropriate steps to not succumb to their use," wrote Bishop Oscar Cantu of Las Cruces, who chairs the U.S. bishops' Committee on International Justice and Peace.

In a May 11 letter to U.S. National Security Advisor Susan Rice, the bishops said leaders should consider the "full cost" of drone warfare.

"Drones provoke anxiety among populations where there are targets, inflicting psychological damage on innocent civilians who live in constant fear they may be hurt or killed and listed as 'collateral damage.' This fear and civilian casualties feed into increasing hostility towards the United States so that many say the use of armed drones in these targeted killings is counterproductive to establishing and sustaining longer-term security relationships with countries where drones are used," they said.

Armed drone technology has the potential for "much harm," the bishops continued. More countries are acquiring drones and government spending on the technology is rapidly increasing.

Armed drones may be used excessively due to their low initial costs, the bishops warned. This risks expanding conflict zones and increasing the likelihood for war. The use of surveillance drones by China, Japan and the Philippines have worsened tensions over disputed territories.

The bishops' letter noted the dangers of wrongly targeted drone attacks, as found in the Central Intelligence Agency's January 2015 report that one of its drones was responsible for the inadvertent death of an American and an Italian aid worker.

The bishops voiced concern that civilians killed in drone attacks are being counted as extremists. They rejected the U.S. administration's justification of "signature strikes," saying this means individuals are targeted by drones "not because of who they are, but because of their behavior or associations."

They called for the U.S. administration to outline a targeting criteria that distinguishes targets from innocent civilians. Such criteria can help avoid the "hostility and radicalization" that results when civilians are harmed.

"As weapons technology becomes more sophisticated, the need for an internationally recognized ethical and moral framework governing their use becomes more urgent," the bishops added.

They called for U.S. leadership in restrictions on "the production, use and proliferation of drones in general, and of armed drones in targeted killings in particular."

The bishops recommended that international standards limit armed drone use to avoid targeted killings that are "assassinations" or "extrajudicial killings."

"There should be a clear and transparent line of authority and oversight regarding the use of armed drones in targeted killings, and specifically over any decision to use them in situations where there has been no declaration of war, so that in cases of humanitarian violations, the appropriate individuals and offices may be held accountable."

The bishops also criticized any automation of armed drones that involves killing."The use of fully autonomous killer drones raises serious questions of moral accountability," they said.

The bishops' latest letter echoes the words of other Catholic leaders.

Archbishop Silvano Tomasi, the Holy See's Permanent Observer to the United Nations in Geneva, in November 2014 told a U.N. meeting on conventional weapons that leaders must address questions surrounding drones "before they become an additional source of greater destabilization when the international community needs more than ever stability, cooperation and peace."