The United States has warned Burma's military rulers that they must cooperate with UN mediator Ibrahim Gambari or face increased pressure from the Security Council.

US ambassador Zalmay Khalilzad told reporters after closed-door consultations with Gambari that the 15-member council expected "concrete results" from the UN troubleshooter's visit to Burma next month.

"My message to the regime is to take advantage of Mr Gambari's visit," the US envoy said.

"Absent political progress, we see the potential for increased political instability and the council cannot remain indifferent to that."

He added that the ruling junta must "turn a new page" and agree to a political roadmap for elections in 2010 as well as to the release of political prisoners, including opposition leader Aung San Suu Kyi.

"If there is not progress on these issues ... we would have to look at other measures, bringing more pressure to bear on the regime," Khalilzad said.

"Things have gone backwards in Burma over the last six months," British Ambassador John Sawers said ahead of the council meeting.

"We're in a difficult situation in the sense that the Burmese government has not responded to the demands of the international community."

Vietnam's UN Ambassador Le Luong Minh, the council chair this month, reaffirmed the 15-member body's support for Gambari's mission, set for mid-August, and said members wished him "success in his mission".

The visit had to be postponed after Cyclone Nargis struck the country in May, leaving at least 138,000 missing or dead.

Gambari, the UN's pointman in efforts to bring about reconciliation between the military regime and its pro-democracy foes, last visited Burma in March.

It was his third visit there since the regime launched a deadly crackdown on pro-democracy protests last September, killing at least 31 people.

On Wednesday, UN chief Ban Ki-moon also called for strong cooperation from Burma, after convening a meeting of the so-called Group of Friends to discuss Gambari's visit.

The group specifically said "tangible progress" was expected "with regard to the resumption of dialogue between Aung San Suu Kyi and the government, the credibility of the electoral process, and the regularisation of engagement with the good offices of the Secretary General".

The meeting of the group, which was set up last December, brought together Australia, Britain, China, France, India, Indonesia, Japan, Norway, Russia, Singapore, South Korea, Thailand, the United States, Vietnam, the European Community and the European Union.

Meanwhile, the US Congress has voted to renew legislation banning all imports from Burma and sent it for President George W Bush's signature.

The Burmese Freedom and Democracy Act renews a sanctions regime imposed since 2003 over the suppression of opposition leader Aung San Suu Kyi's democracy movement.

The legislation maintains sanctions on the ruling military generals until the regime makes fundamental changes, including steps towards reconciliation and democratisation, an end to attacks on ethnic minorities and the release of all "prisoners of conscience".

Two days ago, the US Congress cleared legislation intended to keep Burma's gems, including jade and rubies, from entering US markets via third-party countries.

Despite the long-standing ban on all imports, gems from the impoverished country have entered the United States via nations such as Thailand, China, Taiwan, Malaysia and Singapore, rights groups say.