Hillary Clinton's campaign has declined an invitation to a proposed Fox News-hosted Democratic presidential debate that her primary opponent Bernie Sanders tentatively accepted last week.

The campaign released a statement Monday, almost a week after Fox News invited both Democratic presidential candidates to a final debate in California before the June 7 primaries.  

"We have declined Fox News' invitation to participate in a debate in California," Clinton Campaign Communications Director Jennifer Palmieri said in a statement. "As we have said previously, we plan to compete hard in the remaining primary states, particularly California, while turning our attention to the threat a Donald Trump presidency poses.

"We believe that Hillary Clinton's time is best spent campaigning and meeting directly with voters across California and preparing for a general election campaign that will ensure the White House remains in Democratic hands."

“Naturally, Fox News is disappointed that Secretary Clinton has declined our debate invitation, especially given that the race is still contested and she had previously agreed to a final debate before the California primary," Bill Sammon, Fox News VP and Washington Managing Editor said in a statement. 

Sanders’ campaign tentatively accepted the invitation last week under the assumption they could reach a "mutual agreement” with Clinton.

Sanders said in a statement Monday night he was "disappointed but not surprised" by Clinton's decision not to participate. 

“The state of California and the United States face some enormous crises. Democracy, and respect for the voters of California, would suggest that there should be a vigorous debate in which the voters may determine whose ideas they support. I hope Secretary Clinton reconsiders her unfortunate decision to back away from her commitment to debate.

"I also would suggest that Secretary Clinton may want to be not quite so presumptuous about thinking that she is a certain winner. In the last several weeks, the people of Indiana, West Virginia and Oregon have suggested otherwise," he said.

The Vermont senator echoed his statement at a campaign apperance in Santa Monica, Calif. Monday night. 

"I gotta tell you this," Sanders said, "I think it is a little bit insulting to the people of California, our largest state, that she is not prepared to have a discussion with me about how she will help the Californians address the major crises that we face."

The campaigns earlier this year agreed in principle to hold a May debate.

California is one of six states holding Democratic primaries or caucuses on June 7. The others are Montana, New Jersey, New Mexico, North Dakota and South Dakota.