China and Russia signalled last night that they would block any UN sanctions against Burma as a UN envoy headed to Singapore to try to get a visa to enter the country.

The UN Security Council gathered in emergency session to discuss the crackdown on street protests in the country, amid calls from the US and the European Union nations for international action. After separate talks in New York, US and EU ministers condemned the violence against peaceful demonstrators and asked the 15-nation Security Council to “consider further steps including sanctions” against the junta.

But Wang Guangya, China’s UN ambassador, told the closed door Security Council meeting that, while Beijing favoured stability and national reconciliation in Burma, the crisis was an internal matter. “We believe sanctions are not helpful for the situation down there,” Mr Wang said.

Vitaly Churkin, Russia’s UN Ambassador, said what Burma needed first was a “return to security”.

Ibrahim Gambari, the UN troubleshooter, was due to fly to Singapore to press for a visa to make his first visit to Burma since he met the democracy leader Aung San Suu Kyi last year in an unsuccessful attempt to secure her release from house arrest.

Ban Ki Moon, the UN Secretary-General, urged the Burmese regime to co-operate with Mr Gambari's mission and repeated his call for the “utmost restraint toward the peaceful demonstrations taking place”.

Zalmay Khalilzad, Washington's UN ambassador, also called on Burma to let Mr Gambari in without delay. “It is very important that this be done on an urgent basis,” Mr Khalilzad said. “It would not be good for Mr Gambari to visit grave sites after many more Burmese have been killed.”

Gordon Brown had earlier added his voice to the growing chorus of criticism, when he warned the reclusive regime in Burma that “the whole world” was watching the stand-off.

“Its illegitimate and repressive regime should know that the whole world is going to hold it to account,” the Prime Minister said, speaking at the Labour Party conference in Bournemouth. “The age of impunity in neglecting and overriding human rights is over.”

The pro-democracy demonstrations and crackdown by the army could not have come at a worse time for the reclusive military leadership in Burma.

World leaders were assembled in New York when the demonstrations in Rangoon gathered momentum and the struggle has dominated the debate at the UN General Assembly.

President Bush has announced fresh US sanctions against Burma, the European Union is strengthening its measures against the regime and further action may follow from the UN Security Council meeting.

France, which currently holds the presidency of the UN Security Council, appeared eager to set the example. President Sarkozy called last night on French businesses, including the oil giant Total, to freeze investments in Burma in response to the crackdown.

Burma was forced on to the formal Security Council agenda last September by a procedural vote. China, Russia, Qatar and Congo voted against. China and Russia also vetoed a US-sponsored resolution in January calling for Burma to stop persecuting minority and opposition groups and to start a political dialogue.

China, Burma’s largest trading partner, is regarded as crucial to the international response. In the past it has refused to interfere in the country’s internal affairs but may be softening its position.

The West hopes that Beijing, which is hosting next year’s Olympics, will take a tougher stand against Burma, as it has done recently in relations with Sudan and Zimbabwe.

“China has made some significant concessions recently on its links with Sudan, but it has not gone that far on its links with Burma,” said David Mathieson, a Burma consultant for Human Rights Watch.

“If things heat up, that is not going to look good for China in the lead up to the Olympics at all,” he said.

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