Hong Kong's security chief, Regina Ip, has resigned following criticism of her handling of a controversial anti-subversion bill.
Regina Ip was one of the least popular of Mr Tung's inner circle
A government statement said Ms Ip had offered to resign "for personal reasons" on 25 June - well before huge street protests forced the government to back down over the bill - known as Article 23.
"After careful consideration, I have decided to respect her wish
and accept her resignation," Chief Executive Tung Chee-hwa said.
But analysts are sure to link the departure of 52-year-old Ms Ip - a key supporter of the bill - with the government's current political problems.
Mr Tung's administration has been under fire since the beginning of July, when half a million people marched through the territory to voice their concerns that the bill would undermine political, religious and media freedoms.
The public outcry led Mr Tung to delay trying to get the bill approved by the legislature.
Outlaws: Reporting state "secrets"
Criticism of Beijing authority
Access to "subversive" material
Threatens currently legal groups, such as Falun Gong
Since then, there have been increasing calls for the unpopular Mr Tung to resign, or at least shake-up his government.
But Mr Tung is also under pressure from Beijing, which regained sovereignty of Hong Kong from Britain in 1997 and wants the anti-subversion bill passed.
Beijing's top representative to the territory, Gao Siren, said on Wednesday that continued opposition to the anti-subversion bill would harm the economy.
"Hong Kong is a city of business, not of politics," he told the China Daily, a state-run Chinese newspaper.
In Ms Ip's resignation statement, issued on Wednesday, she expressed her concerns that the anti-subversion bill was "not completed as scheduled".
"As a Chinese national and the secretary for security, I
sincerely believe I have a responsibility to actively
promote this highly important legislative task," she
said, according to the Associated Press news agency.
In another problem to beset Hong Kong's beleaguered government, the Justice Department said on Wednesday that it was considering whether to prosecute financial chief Antony Leung.
Mr Leung bought a luxury car in February just weeks before he upped the tax on new vehicles, provoking widespread public criticism.
Analysts say that Mr Tung may use the Antony Leung affair as an excuse to reshuffle his cabinet to score points with a disgruntled public.