NEW YORK (AP) — MSNBC says prime-time TV host Keith Olbermann will be back on the air today, ending his suspension for violating NBC's rules against making political donations after two shows.

MSNBC's chief executive Phil Griffin said late on Sunday that after several days of deliberation, he had determined that two days off the air was "an appropriate punishment for his violation of our policy."

The left-leaning cable network's most popular personality acknowledged donating $2,400 apiece to the campaigns of Kentucky Senate candidate Jack Conway and Arizona Reps. Raul Grijalva and Gabrielle Giffords. NBC News prohibits its employees from making political donations unless an exception is granted in advance by the network news president. In this case, Olbermann's bosses didn't know about them until being informed by a reporter.

"We look forward to having him back on the air on Tuesday night," Griffin said in a statement.

Liberal groups had taken on Olbermann's suspension as a cause. An online petition calling for his reinstatement, run by the Progressive Change Campaign Committee, had exceeded 300,000 signatures on Sunday, and Michael Moore had tweeted his support. The committee's Adam Green said Griffin was repeatedly e-mailed updates on the petition drives.

"Progressives proved that when one of our own are targeted, we will have their backs," he said.

Left unanswered is the question of why Olbermann would do something he undoubtedly knew would be provocative, or whether he was trying to make a statement against NBC's policy. He did not immediately return an e-mail message seeking comment on Sunday.

On his Twitter page, Olbermann wrote: "Greetings from exile! A quick, overwhelmed, stunned THANK YOU for support that feels like a global hug."

The incident raised questions about how long-standing rules designed to preserve the appearance of objectivity for news organisations fit at a time that cable news networks, most prominently Fox News Channel and MSNBC, have increased their popularity through prime-time programmes that dispense with any notion of impartiality.

"What we've seen in the last five years is the rise of these personalities that eclipse the journalism that these organisations do," said Kelly McBride, ethics group leader at the Poynter Institute journalism think tank.

Many mainstream news organisations take these rules dead seriously. National Public Radio subjected itself to some teasing this fall when it issued a memo forbidding its personnel from attending comic Jon Stewart's rally in Washington last month, but NPR didn't want reporters seen at an event that some people could interpret as political, unless the reporters were covering it.

Olbermann's fans note that he's made no secret of his support for Democrats on his prime-time "Countdown" show. So why should he be suspended for putting his money where his mouth is?

His prime-time MSNBC colleague, Rachel Maddow, said on her show on Friday night that Olbermann should be reinstated. Her bosses were told she'd be saying that before going on the air, however.