Image caption Olbermann played a key role in election coverage

The US broadcasting network MSNBC has suspended prime-time host Keith Olbermann for making political contributions.

The Politico news website said he had contributed to the campaigns of three Democratic candidates.

MSNBC President Phil Griffin said Olbermann had been suspended without pay.

During coverage of the US mid-term elections, Olbermann was one of the network's key presenters.

"Mindful of NBC News policy and standards, I have suspended him indefinitely without pay," Mr Griffin said, according to a statement quoted by the Huffington Post.

With Rachel Maddow, Olbermann has been one of the most prominent hosts on the network, which analysts say has come to be seen as liberal-aligned.

The BBC's Jonny Dymond, in Washington says that while America's 24-hour news channels are increasingly politicised and polarised, it appears there is a limit.

The suspension comes just a couple of weeks after America's national radio network, NPR, sacked one of its commentators for saying that he became nervous when flying with passengers wearing what he called "Muslim garb".

Juan Williams' dismissal raised an outcry on the political right which accused the network, which receives some federal funding, of liberal bias.