|Pakistan's human rights panel has documented more than 1,100 violent deaths Karachi in the first half of 2011 [AFP]
At least 10 passengers were killed and 20 others injured on Wednesday when armed men opened fire on two buses in Pakistan's port city of Karachi, officials said.
"Unknown armed men intercepted two buses on a road in Banaras Chowk neighbourhood and shot indiscriminately on the passengers, killing at least 10 and wounding 20 others," a provincial home ministry official told AFP news agency.
The inspector general of police told Al Jazeera that 15 other people were targeted and shot dead in different areas across Karachi – bringing the death toll on Thursday to 25.
The fresh wave of violence in the city began on Tuesday.
The violence, which broke out in Orangi Town, later spread to Lyari, Baldia Town, Site and Gulshan-i-Iqbal areas.
Pakistan attack raises security fears
Police said armed men hijacked one of the minibuses from Rashid Minhas Road and shot five passengers - three of whom were relatives, in the head.
The assailants managed to escape after dumping the vehicle in the Ziaul Haq Colony in Gulshan-i-Iqbal.
City officials blame the third straight day of violence on political and ethnic tensions.
Police claimed it arrested over 100 individuals suspected of being involved in the violence.
Karachi is frequently plagued by sectarian killings, crime and kidnappings.
On Tuesday, the Human Rights Commission of Pakistan said it had documented the violent deaths of more than 1,100 people in Karachi in the first half of 2011. Some 490 of these were targeted killings on political, ethnic or sectarian grounds.
The figures do not include an estimated 42 people killed in the first week of July, one of the most violent periods in Karachi this year.
"The alarming rise in targeted killings and general insecurity in Pakistan over the past two years reflects a grave law and order crisis in the country," said Sam Zarifi, Asia-Pacific director at Amnesty International.
"Even when investigations have been opened in a few high-profile cases, they have either been inadequate or have failed to address the systemic problems leading to impunity."