Google has fired 28 employees involved in protests over the tech company's cloud computing contract with the Israeli government, according to statements from the company and campaigners.

The workers held sit-ins at the company's offices in California and New York over Google's $1.2 billion contract to provide custom tools for Israeli's military. They were fired on Wednesday evening after police earlier arrested nine people.

Google said "a small number of employee protesters entered and disrupted a few of our locations."

"After refusing multiple requests to leave the premises, law enforcement was engaged to remove them to ensure office safety," Google said.

The company said it carried out "individual investigations that resulted in the termination of employment for 28 employees, and will continue to investigate and take action as needed."

The group behind the protests, No Tech for Apartheid, disputed Google's version of events, saying the company fired people who didn't directly participate.

The company's claim that the protests were part of a longstanding campaign by groups and "people who largely don't work at Google" was untrue, the group said.

The group posted photos and videos on social media showing workers in Google offices holding placards and sitting on the floor, chanting slogans.