Western leaders expressed dismay Monday at Zimbabwe's decision to pull out of the British Commonwealth rather than endure a suspension, and insisted President Robert Mugabe was only pushing his troubled southern African nation deeper into isolation.

Mugabe's government made good on his threat to leave the bloc of Britain and its former colonies late Sunday, just hours after a tense 52-nation Commonwealth summit (search) extended Zimbabwe's 18-month suspension for alleged widespread abuses of civil liberties.

"It's quits, and quits it will be," Mugabe's government declared in a statement from Zimbabwe.

In a major snub for Zimbabwe's leader, Commonwealth heads of state meting in Abuja, Nigeria had rejected a push led by Zimbabwe's southern African neighbors to lift the suspension.

The Commonwealth — whose nations represent nearly one-third of the world's 6 billion people — banned Mugabe from its decision-making councils in 2002 after he was accused of using massive force and fraud to win re-election at home.

Several African and other developing nations had campaigned for Zimbabwe's reinstatement, saying dialogue, not isolation, was the way to bring change.

Sunday's accord to extend the suspension averted a rift between the Western and developing nations in the Commonwealth.

In the wake of Zimbabwe's pullout, Britain, Australia and New Zealand — leading advocates of standing by the suspension — insisted it was Mugabe who chose to cut off his nation from the rest of the world.

"It is unfortunate that President Mugabe has decided to shut the door on those who could help him rehabilitate his nation in the eyes of the world," New Zealand Prime Minister Helen Clark (search) said Monday. "Zimbabwe's government seems determined to thumb its nose at international opinion."

She called on Zimbabwe to reconsider. "The Zimbabwe government's decision to withdraw is not a disaster for the Commonwealth. It is an indictment of Zimbabwe's government that it has chosen this path."

A spokesman for Australian Prime Minister John Howard (search) said Commonwealth leaders had been informed of Zimbabwe's pullout even before they agreed to extend the suspension.

"The Commonwealth has taken a stand on principles which is very welcome — but ultimately it is a decision for the Zimbabwe government," the spokesman said on customary condition of anonymity.

Under the Commonwealth's agreement, Nigerian President Olusegun Obasanjo had been charged with monitoring Zimbabwe on behalf of the bloc.

The Nigerian leader — himself marking his nation's return to the bloc after suspensions under past Nigerian military regimes — was to report back to a six-country suspension-review panel if and when he saw signs of improvement.

Obasanjo had told reporters Sunday he planned to visit Zimbabwe himself to meet government and opposition officials.

At the time, Obasanjo insisted Zimbabwe's outcast status would be lifted quickly.

In Zimbabwe's statement, Mugabe's government insisted it would accept nothing short of full reinstatement.

"Anything you agree on Zimbabwe which is short of this position, no matter how sweetly worded, means Zimbabwe is still a subject of the Commonwealth. This is unacceptable," Zimbabwe said.

Many African leaders stayed publicly silent through most of the debate on Zimbabwe, and kept that silence Monday. South African President Thabo Mbeki was believed to be a behind-the-scenes leader of those pushing for reinstatement.

Commonwealth officials insisted the suspension — with the new monitoring mechanism adopted Sunday — was meant to help Zimbabwe work its way back into the Commonwealth.

"It is not something the Commonwealth wanted," bloc spokesman Joel Kibazo told The Associated Press, calling Zimbabwe's pullout "disappointing news."

"This was supposed to be seen as a way forward, not a way backward," Kibazo said.