San Francisco's Bay Area Rapid Transit system (Bart) and rail trade unions reached a tentative agreement on a new contract on Monday night, ending a crippling four-day strike.

Union officials announced the pay deal, which still required approval by union members and the company's board of directors.

Bart spokeswoman Alicia Trost said limited service would resume at 4am.

Workers had walked off the job on Friday after talks broke down.

The contentious talks betweean Bart and its two largest unions had dragged on for six months - a period that saw two days-long strikes and contentious negotiations.

Bart general manager Grace Crunican said: "The public expects us to resolve our differences and to keep the Bay Area moving."

She added that there would be no immediate announcement on the details while union leaders explained the agreement to their members, but that the deal was more than they wanted to pay.

A settlement was reached just two days after two track workers were killed in a Bart train accident in Walnut Creek.

Federal investigators said on Monday the train had been run by a Bart trainee driver.

Union officials had previously cautioned the company that training managers to operate trains during the walkout could be dangerous.

Amalgamated Transit Union Local 1555 president Antonette Bryant expressed her condolences to the families of the workers who were killed.

"We did not want to strike," she said "and we are glad to have a tentative agreement that we feel will work for all parties."