NEW YORK (AP) - MSNBC host Keith Olbermann announced Friday that he is leaving the network and has taped his last “Countdown” show.

MSNBC issued a statement that it had ended its contract with the controversial host, with no further explanation. Olbermann hosted the network’s most popular show, but his combative liberal opinions often made him a target of critics.

Olbermann did not explain why he was leaving.

“MSNBC thanks Keith for his integral role in MSNBC’s success and we wish him well in his future endeavors,” the network said.

A spokesman said Phil Griffin, MSNBC’s president, would not comment on Olbermann’s exit. Spokesman Jeremy Gaines would say only that the acquistion of NBC Universal by Comcast, which received regulatory approval this week, had nothing to do with the decision.

Olbermann was suspended without pay from the network for two days in November for donating to three Democratic candidates, which violated NBC News’ policy on political donations. Olbermann complained that he was being punished for mistakenly violating an inconsistently applied rule that he had known nothing about.

The host apologized to fans — but not to the network.

Olbermann, before leaving the show with a final signature toss of his script toward the camera, thanked his audience for sticking with him and read a James Thurber poem.

“This may be the only television program where the host was much more in awe of the audience than vice versa,” he said.

He thanked a series of people, including the late Tim Russert, but pointedly not Griffin or NBC News President Steve Capus.

Olbermann’s prime-time show is the network’s top-rated. His evolution from a humorous look at the day’s headlines into a pointedly liberal show in the last half of George W. Bush’s administration led MSNBC to largely shift the tone of the network in his direction, with the hirings or Rachel Maddow and Lawrence O’Donnell in primetime.