Press Secretary Jay Carney's statement called it "a despicable and outrageous act against innocent civilians, and the United States resolutely opposes all forms of terrorism."
The attack occurred in western China in Urumqi, the capital of Xinjiang province and a city of over 3.3 million. It is home to the Muslim Uighur minority, members of whom are presumed to have carried out the attack.
The area has seen recent ethnic violence, with Uighurs resentful of taking orders from the Beijing government, as well as an influx of Han Chinese to the area, which Uighurs fear is an impediment to maintaining their culture.
Chinese president Xi Jinping promised to "severely punish" the offenders in Wednesday's attack, and to restore calm to the area.
The attack came a day after 39 people were sentenced to jail terms for spreading terrorism in the region, highlighting the Chinese government's "strike first" approach to clamping down on attempts at ethnic and regional autonomy.
"Beijing's high-pressure policy in Xinjiang has descended to a vicious circle. More crackdown will breed more violent attacks," predicted Hu Xingdou, economics professor at Beijing Institute of Technology.
The bombings Wednesday also showed a shift in tactics, from violent rioting and clashes between ethnic groups to deadly civilian attacks. Placing new restrictions on Xinjiang residents will likely impede attempts to improve the region's economic conditions.
"With the perception that things are spiraling out of control in Xinjiang, one question is whether Xi's economic plans for the province will fail at the expense of fighting extremists," said James Leibold of La Trobe University in Melbourne, Australia.