A US State Department official was set to testify on Monday about how much convicted soldier Bradley Manning's leaks of classified diplomatic cables to the WikiLeaks website hurt ties between Washington and its allies as well as global intelligence-sharing methods.

Judge Colonel Denise Lind on July 30 found Army Private First Class Manning, 25, guilty of 19 criminal counts related to the leaks, the largest unauthorized release of secret US data in the nation's history.

Manning was found not guilty of aiding the enemy, the most serious charge he faced, but the crimes still carry penalties that could lead to up to 136 years in prison.

The sentencing phase, which began last week, was set to resume on Monday and is expected to last at least until Aug 9, military officials said.

Military prosecutors are expected to call Patrick Kennedy, a veteran State US Department official who was part of an "Information Review Task Force" set up in the wake of the leak, to assess damage to US-foreign relations or any other fallout.

"The post-WikiLeaks environment reminds us that technology is a tool to execute solutions but is not in itself the answer," Kennedy, the Under Secretary for Management, told the US Senate Committee on Homeland Security and Governmental Affairs in March 2011.

"Simply put, we must more consistently sort out what we share before determining how we share it," Kennedy said, adding that national security officials must do a better job confining intelligence that could threaten security.

Also on Monday, Lind said she will rule or issue guidance on the defense motion to exclude testimony that uses "chain of events" reasoning to suggest future potential damage done by Manning, rather than specific harm he has directly caused.

Manning's lawyers, who have portrayed him as naive but well intentioned, were expected to ask Lind for leniency in sentencing. They argue the soldier's aim was to provoke a broader debate on US military policy, not to harm anyone.

Manning was in Baghdad in 2010 when he was arrested and charged with leaking files, including videos of a 2007 attack by a US Apache helicopter gunship in Baghdad that killed a dozen people, including two Reuters news staff.

Other files contained diplomatic cables and secret details on prisoners held at Guantanamo Bay.

Most of the leaked diplomatic cables originate after 2005, when a new information sharing system was adopted to address intelligence failings exposed by the Sept 11, 2001, attacks.

Kennedy is among a parade of prosecution witnesses to testify for the government, including one who said Manning's leak undid part of a US intelligence-sharing system, before Manning's lawyers will also have a turn to call their own witnesses.

Another US State Department official, the former ambassador to Belarus, Michael Kozak, testified on Friday that the leaks led to foreign informants being moved over fears for their safety.

Access to classified information remains a sensitive subject after Edward Snowden, a US intelligence contractor, revealed the National Security Agency's secret program to collect phone and Internet records.

Reuters