A multi-ethnic coalition has demanded more racial diversity both in front of and behind the cameras at US television network CBS.

The group, which conducts an annual study into diversity on US television, said all the major networks were at best mediocre in their efforts to reform.

But it gave CBS a grade of D-minus - the lowest overall grade on the group's annual report card.

Moonves was singled out for criticism

CBS has said the accusations are "crazy" and has disputed the consortium's findings.

In letters to board members of CBS' parent company and major advertisers, the coalition of ethnic diversity groups said CBS president Leslie Moonves deserved much of the blame.

"Leslie Moonves was never that interested in significantly increasing opportunities for Latinos, Asian Americans and Native Americans," wrote Karen Narasaki, the head of the consortium.

"Now he appears to have lost interest altogether.

"We're asking corporate America to join us in a partnership to make this happen."

'Dedicated'

CBS countered with a statement disputing the coalition's findings. It also denounced the criticism of Mr Moonves as "crazy".

"Leslie is the most dedicated and focused diversity-conscious executive in the business," said the network's vice president for diversity, Josie Thomas.

"Every executive and every manager at CBS is taking ownership of this issue."

Ms Thomas pointed out that three out of the four top executives in the network's development ranks - senior vice presidents for drama, movies and miniseries and reality TV - were from minorities.

"I think that speaks volumes about commitment at the top," she said.

Last year's lowest ranked network, Walt Disney Co.-owned DIS.N ABC, rose from a D-minus to a C-minus, while last year's winner, NBC, fell from a C to a D-plus.

The consortium comprises the National Latino Media Council, the Asian Pacific Americans Media Council, and American Indians in Film & Television.