Tony Blair is facing a battle with his Commonwealth partners over the future of Robert Mugabe's regime in Zimbabwe.

The prime minister hopes to use a meeting of Commonwealth heads in Nigeria to press the case for regime change in Harare.

Alongside foreign secretary Jack Straw, Blair will launch a fresh push against the Zanu PF regime.

Speaking as he headed to the summit, Blair delivered an uncompromising message to the other 53 Commonwealth leaders.

"The key thing is to maintain the suspension of Zimbabwe from the Commonwealth because that sends the right signal of strong disapproval for what is happening in Zimbabwe at the present time," he told reporters.

"The Commonwealth has got a limit to the power that it can have. But it is far better to send a signal than do nothing."

The British-led effort, which is supported by Australia, could divide the Commonwealth along racial lines.

But the prime minister has indicated that he does not wish the Zimbabwe row to overshadow the rest of the talks.

Many African leaders believe it is time Zimbabwe was brought in from the cold.

The country has been suspended from the Commonwealth following a rigged election and a growing number of human rights abuses.

Britain believes the suspension, coupled with EU sanctions on travel and finance, could bring about a change in leadership.

The UK will say that Commonwealth chiefs should use their influence to seek a change in leadership - although Canada is said to back a compromise which could see Zimbabwe's suspension ended within two years.

The row threatens to overshadow a summit where issues such as Aids and polio will also be high on the agenda.

Blair has hit back at those who accuse Britain of colonialism, claiming some African leaders are "defending the indefensible".

"I certainly don't favour doing anything that diminishes the obligation to make change there because change is so obviously in the interests of the people," he said.

As the prime minister left London on Thursday, Number 10 blamed the deteriorating situation in Zimbabwe on the Mugabe leadership.

"There is a growing consensus at the top level that Zimbabwe has failed to meet the benchmarks that the Commonwealth had laid down," said the official spokesman.

"It will be good for the people of Zimbabwe who are facing a crisis which is not a result of any outside interference. It is a government-made crisis," said Number 10.

The Liberal Democrats urged the prime minister to press his case during the weekend talks.

"The Commonwealth must stand firm against any effort by the Mugabe regime to have Zimbabwe's suspension lifted," said Menzies Campbell.

"Any government which practices political intimidation, restricts press freedom and pays no regard to human rights cannot expect to remain within an organisation which is committed to democratic principles."

Britain will also use the summit to call for Pakistan to be readmitted to the Commonwealth.

Pakistan was suspended after General Musharraf's 1999 military coup but the country has played a key role in ousting the Taliban from Afghanistan.

Britain and Australia are calling for Pakistan to be allowed back but African countries have rejected the move.

The Queen, who is head of the Commonwealth, arrived in the country earlier this week ahead of the formal opening of the summit.The rise of Islamic terrorist groups in the region mean the four day event is subject to tight security.