A special ministerial group set up to safeguard democratic standards harshly criticised President Pervez Musharraf for his three-week-old state of emergency and suspended Pakistan's membership late on Thursday.

"The situation in Pakistan continued to represent a serious violation of the Commonwealth's fundamental political values," a statement said.

Pakistan is not attending the Kampala summit but Foreign Ministry spokesman Mohammad Sadiq told Reuters in Islamabad that his country deeply regretted the suspension by the Commonwealth Ministerial Action Group (CMAG).

"The CMAG decision is unreasonable and unjustified. Pakistan will review its association and further cooperation with the organisation," he said.

Zimbabwe, suspended in 2002 over flawed elections, withdraw from the Commonwealth the following year.

It was the second time Pakistan had been suspended after being barred when Musharraf first seized power in 1999. It had been reinstated in 2004.

The angry reaction from Islamabad underlined the huge international pressure on Musharraf to fully lift the emergency rule he imposed on November 3.

While Commonwealth suspension has few immediate practical effects, analysts say it could further isolate Musharraf, a key U.S. ally in the war against Islamic militancy, discourage foreign investment and undermine him domestically, where he is trying to fend off major opposition challenges to his continuing rule.

The summit here will also discuss Fiji, which has been suspended since a military coup in 2006. The Pacific island nation has promised elections in 2009 but critics say little democratic progress has been made.

CLIMATE CHANGE

One of the biggest issues for discussion here is climate change and its impact on Commonwealth members, especially small island states threatened by rising water levels.

Experts say Africa also risks being left behind in efforts to combat warming, which could have a disastrous effect on crops on the continent through drought.

"One of the biggest challenges we face is climate change. The consequences ...are far ranging," said outgoing Commonwealth chairman Lawrence Gonzi, the prime minister of Malta, in an early address after the summit was opened by Queen Elizabeth.

"Small island states like my own country are particularly vulnerable, but the need to adapt is one that faces all countries," he said.

Many Commonwealth leaders, eager to show their relevance as a unique body cutting across regional groupings, believe they can issue an influential statement before a meeting of world environment ministers in Bali next month which will discuss a new deal to replace the U.N.'s Kyoto protocol.

Britain is pushing hard for a strong statement.

"We hope Commonwealth heads will send an unequivocal message that to achieve climate security we need a high-ambition, U.N.-based global framework with developed countries taking on binding emission reduction commitments," Foreign Secretary David Miliband said before the meeting.

But diplomats said Canada's conservative government, which believes its commitments under the Kyoto treaty are impractical, would resist such a tough statement. Canada is a big oil producer.

Australia is a major CO2 emitter but, with an election coming this weekend, has not sent a senior delegation to Kampala. Pacific island nations are furious with Australia for refusing to ratify Kyoto.