Washington, April 2 Self-styled Democratic Socialist Bernie Sanders has said his presidential primary opponent Hillary Clinton owed him and his campaign an apology over an ongoing spat about donations from the fossil fuel industry.

\"Secretary Clinton, you owe us an apology. We were telling the truth,\" Sanders said on Friday in response to accusations from Clinton\'s campaign that he and his campaign had been \"lying\" and misconstruing Clinton\'s relationship with the oil and gas industry.

\"The truth is that Secretary Clinton has relied heavily on funds from lobbyists working for the oil, gas, and coal industry,\" NBC News quoted Sanders as saying in front of a crowd of about 2,200 people in Sheboygan South High School.

Sanders argued that Clinton\'s campaign has received \"more than $4.5 million from the fossil fuel industry\" and said \"57 oil, gas, and coal industry lobbyists have directly contributed to her campaign\", citing an analysis done by the environmental organization Greenpeace.

The Clinton team quickly responded, saying they would not apologise.

Clinton\'s campaign said Sanders was going out of his way to \"deliberately mislead voters rather than debate the issues.\"

\"We will not apologize for calling out these kinds of schemes for what they are: a desperate move from a campaign that has clearly decided that the only hope for a path to victory is through misleading attacks,\" Clinton campaign communications director Jennifer Palmieri said in a statement to NBC News.

Palmieri also said the Sanders campaign has received campaign contributions from \"individuals who work for oil and gas companies\".

The controversy started on Thursday when a video came out on social media showing an activist from Greenpeace confronting Clinton on the issue of fossil fuel industry contributions at a rally at SUNY Purchase, New York.

\"I have never ... I am so sick, I am so sick of the Sanders campaign lying about me. I am sick of it,\" she said forcefully,\" she said.

Bernie Sanders demands apology from Hillary