Security forces cordon off the blast site in southwest Pakistan's Quetta, April 24, 2013. At least four people were killed and 37 others injured on Tuesday night in a series of bomb blasts followed by a suicide attack in Pakistan's southwestern provincial capital of Quetta, local media reported. (Xinhua/Mohammad)

A Pakistani soldier inspects the blast site in southwest Pakistan's Quetta, April 24, 2013. At least four people were killed and 37 others injured on Tuesday night in a series of bomb blasts followed by a suicide attack in Pakistan's southwestern provincial capital of Quetta, local media reported. (Xinhua/Mohammad)

Residents gather at the blast site in southwest Pakistan's Quetta, April 24, 2013. At least four people were killed and 37 others injured on Tuesday night in a series of bomb blasts followed by a suicide attack in Pakistan's southwestern provincial capital of Quetta, local media reported. (Xinhua/Mohammad)

Residents gather at the blast site in southwest Pakistan's Quetta, April 24, 2013. At least four people were killed and 37 others injured on Tuesday night in a series of bomb blasts followed by a suicide attack in Pakistan's southwestern provincial capital of Quetta, local media reported. (Xinhua/Mohammad)

Residents gather at the blast site in southwest Pakistan's Quetta, April 24, 2013. At least four people were killed and 37 others injured on Tuesday night in a series of bomb blasts followed by a suicide attack in Pakistan's southwestern provincial capital of Quetta, local media reported. (Xinhua/Mohammad)

Security forces cordon off the blast site in southwest Pakistan's Quetta, April 24, 2013. At least four people were killed and 37 others injured on Tuesday night in a series of bomb blasts followed by a suicide attack in Pakistan's southwestern provincial capital of Quetta, local media reported. (Xinhua/Mohammad)

Damaged houses are seen at the blast site in southwest Pakistan's Quetta, April 24, 2013. At least four people were killed and 37 others injured on Tuesday night in a series of bomb blasts followed by a suicide attack in Pakistan's southwestern provincial capital of Quetta, local media reported. (Xinhua/Mohammad)