WASHINGTON - The United States is "deeply concerned" about the recent outbreak of violence in western Kazakhstan, the State Department said on Monday, calling for restraint by all sides.

"We have expressed our condolences for the loss of life and urged restraint by all parties as Kazakhstani authorities work to restore calm," department spokeswoman Victoria Nuland said in a statement.

"We are concerned by reports that some forms of communication were disabled in the wake of these protests, and urge the government of Kazakhstan to quickly and fully restore open lines of communication throughout the country," she added.

She welcomed the government's stated commitment to a "thorough and transparent" investigation into the causes of the violence, calling for punishment of the perpetrators.

The protest in western oil city of Zhanaozen was sparked by clashes between laid-off oil workers and police at a ceremony celebrating Kazakhstan's independence day last Friday, which resulted in at least 10 deaths and 86 injuries, promoting President Nursultan Nazarbayev to declare a 20-day state of emergency in the city the following day.

Protests broke out on Monday in Aktau, another city in the western oil-producing region of the country.