U.S. soldier Bradley Manning's leaks of classified government files had a "chilling effect" on foreign relations, impeding U.S. diplomats' gathering of information, a senior State Department official said Monday.
"Every single embassy" was affected, said Undersecretary of State for Management Patrick Kennedy, who warned about long-term consequences of Manning's 2010 leaks to the anti-secrecy website WikiLeaks.
The releases will have "a chilling effect that will go on for some time," Kennedy said.
Kennedy testified at the sentencing hearing for Manning, who was convicted last week on criminal charges that included espionage. The hearing is to help the court martial determine how long the private first class should be in prison.
Kennedy was part of a panel that assessed the damage Manning caused to U.S. foreign relations by releasing more than 700,000 classified documents and videos.
The unauthorized releases made foreign diplomats, business leaders and other information sources "reticent to provide their full and frank opinions and share them with us," he said, cutting off information that political leaders need to make foreign policy decisions.
At one point, then-Secretary of State Hillary Clinton spoke out publicly in defense of her colleagues who sent the messages, which are known as diplomatic cables.
Attorneys for Manning quoted other U.S. government officials including former Defense Secretary Robert Gates downplaying any fallout from the releases.
Judge Colonel Denise Lind found Manning, 25, guilty on July 30 of 19 criminal counts related to the leaks, the largest unauthorized release of secret data in U.S. history. The files included more than 250,000 State Department cables.
Manning was found not guilty of aiding the enemy, the most serious charge, but the crimes still carry penalties that could lead to up to 136 years in prison.
The sentencing phase began last week and is expected to last at least until Friday, military officials said.
Lind also issued a preliminary ruling that "aggravation evidence" would be disallowed on a case-by-case basis. Aggravation evidence refers to witness testimony on how the WikiLeaks releases are likely to damage U.S. foreign relations.
Under Lind's ruling, the defense must object to any new witness and explain reasons why the testimony should not be allowed. Attorneys plan more argument on the issue on Monday.
Manning's lawyers have portrayed him as naive but well intentioned. They argue the soldier's aim was to provoke a broader debate on U.S. military policy, not to harm anyone.
Manning was a low-level intelligence analyst in Iraq in 2010 when he was charged with leaking files. They included videos of a 2007 attack by a U.S. Apache helicopter gunship in Baghdad that killed a dozen people, including two Reuters news staff.
Most of the leaked diplomatic cables originated after 2005, when a new information-sharing system was adopted to address intelligence failings exposed by the attacks of Sept. 11, 2001.
Kennedy is among a parade of prosecution witnesses to testify for the government, including one who said Manning's leak undid part of a U.S. intelligence-sharing system. Manning's lawyers will also have a turn to call their own witnesses.
Access to classified information remains a sensitive subject after Edward Snowden, a U.S. intelligence contractor, this summer revealed the National Security Agency's secret program to collect phone and Internet records