U.S. authorities are trying to learn why a Vietnamese immigrant opened fire inside an immigration center in the city of Binghamton in the state of New York where just weeks earlier he had attended English classes.

Police said 42-year-old Jiverly Wong walked into the American Civic Association Friday and, without saying a word, shot two receptionists and opened fire inside a classroom filled with immigrants who were studying English.

The rampage left 14 people dead, including the gunman who police say turned the gun on himself after hearing police sirens outside.

City leaders and police said Wong, who lived in the nearby community of Union City, had recently been fired from his job and had been depressed.

Police Chief Joseph Zikuski told reporters Saturday the gunman was also upset because he did not speak English well and felt people "were making fun of him".

Investigators said Wong had been taking English classes at the center until about a month ago.

The ordeal lasted more than 90 minutes, as law enforcement officers surrounded the building and survivors hid in a boiler room and storage closets.  Four people were wounded and 37 others managed to escape.

The center's director, Angela Leach, said it was "unbearable" that such violence had been carried out against an immigrant community that had arrived in America with dreams of a better life.

Separately, a man in Pittsburgh, in the northeastern state of Pennsylvania shot five police officers Saturday during a domestic disturbance call.  Three officers were killed.

Some information for this report was provided by AFP, AP and Reuters.