Image copyright Reuters Image caption The Sanders campaign lost four out of five contests on Tuesday

Bernie Sanders' campaign has begun laying off staff following several losses to Hillary Clinton in Democratic primaries in key states.

His spokesman said that with many primaries over "we no longer require many of the loyal and dedicated state and national support staffers".

After Tuesday's contests, Mr Sanders lacks a path to the Democratic nomination for president.

He has vowed to continue on until the California primary in June.

"We will continue to have a strong and dedicated staff of more than 300 workers who are going to help us win in California and other contests still to come," Mr Sanders' campaign communications director Michael Briggs said in a statement.

The campaign originally had about 1,000 workers, the New York Times reported.

Late on Tuesday, Mr Sanders' campaign said that he would be pushing for a greater role in drafting the Democratic platform.

Many saw the statement as a signal that the Vermont senator would be winding down his campaign in favour of promoting his core issues of income inequality and Wall Street reform.

The campaign will still compete in the coming weeks in contests including Indiana, where Mr Sanders is leading in some polls.

The Sanders campaign boasts an impressive fund-raising operation, bringing in millions of dollars in small donations.

Mr Sanders also has drawn thousands of new voters to the polls including large numbers of young people and independents.

Mrs Clinton and the Democratic Party are hoping to tap into Sanders' fundraising operation and his coalition in the run-up to November's election.