The attack targeted Washington's top diplomat in China, Ambassador Nicholas Burns.
State Department officials provided new details about the breach on Wednesday, Politico reported, citing an unnamed State Department employee.

Most of the 10 affected government email accounts belonged to people working on "Indo-Pacific diplomatic efforts," they said.

Among the most sensitive information stolen were the victims' travel itineraries and diplomatic communications, while 10 Social Security numbers were also accessed during the attack.

The cyberattack was first reported by Microsoft in July, attributing the crime to a "China-based cyber hacker" allegedly backed by the government in Beijing.

A total of 25 organizations were said to have been targeted in the June hack, including the State Department and other government agencies.

Staff said hundreds of thousands of documents may have been involved in the breach, including about 60,000 from the State Department alone.

Senior officials reportedly targeted in the attack include US Ambassador to China Nicholas Burns and Commerce Secretary Gina Raimondo.

Although the US State Department has not yet officially implicated China in the breach, Raimondo has publicly indicated that China is responsible.