* U.N. expert calls for U.S. openness on civilian casualties
* Says missile attacks by unmanned drones "deeply troubling"
* U.S. envoy objects to expert’s comments
By Laura MacInnis
GENEVA, June 3 (Reuters) - The United States should be more forthright about how many civilians die in its overseas wars, and exercise more caution with unmanned drone attacks, a United Nations human rights envoy said on Wednesday.
Philip Alston, U.N. special rapporteur on extrajudicial, summary or arbitrary executions, called the U.S. reliance on pilotless missile-carrying aircraft "deeply troubling" and cited "serious shortcomings" with the U.S. military justice system.
"The government should track and make public the number of civilian casualties," he told the U.N. Human Rights Council.
He recommended that Washington make public the status of all investigations into civilian deaths in its armed conflicts.
The Australian law professor said that U.S. soldiers, Pentagon officials, intelligence agents and private contractors are not being held to account for unlawful killings they commit.
"The government has failed to effectively investigate and punish lower-ranking soldiers for such deaths, and has not held senior officers responsible under the doctrine of command responsibility," he told the 47 member-state forum in Geneva.
"Worse, it has effectively created a zone of impunity for private contractors and civilian intelligence agents by only rarely investigating and prosecuting them," Alston said.
Alston visited the United States last year, before Barack Obama became president. Obama’s Defense Secretary Robert Gates also headed the Pentagon under the George W. Bush administration.
U.S. diplomat Lawrence Richter objected to Alston’s remarks, saying the U.N. investigator did not have the mandate to cover military and intelligence operations related to armed conflict.
Richter told the Human Rights Council that the United States has an extensive legal framework to respond to unlawful killings and is doing all it can to provide information about the deaths that occur in its armed conflicts.
Washington "continues to actively prosecute wrongdoing" overseas, but faces trouble getting witnesses to work with U.S. investigators or travel to testify in U.S. courts, said Richter. "The prosecution of private contractors who commit crimes is an important priority of the Department of Justice," he stressed.
Alston last year angered NATO when he issued an estimate of the number of Afghan civilians killed by foreign and Afghan troops that far exceeded the military alliance’s toll.
On Wednesday, he expressed "strong concern at the continuing problem of preventable civilian casualties, especially in the context of aerial bombing," in Afghanistan and called for "real accountability based on credible independent investigations."
"Targeted killings carried out by drone attacks on the territory of other states are increasingly common and remain deeply troubling," Alston said. "The U.S. government should disclose the legal basis for such killings and identify any safeguards designed to reduce collateral civilian casualties and ensure that the government has targeted the correct person."
Pakistani officials have complained about the drone attacks, calling them a violation of sovereignty and increase resentment towards both Pakistan’s government and the United States.