Wrangling over global warming and Russia-US tensions overshadowed the start of the Group of Eight summit Wednesday as police fought anti-globalisation demonstrators.

Even before an official dinner formally launched the summit, police battled protesters trying to get to the 12-kilometre (seven-mile) long barbed wire fence surrounding the luxury hotel on the Baltic coast where the leaders gathered.

Some 10,000 protesters gathered around the barrier, according to one anti-globalisation group. Eight police were injured in new disturbances as police fired water cannon to disperse demonstrators who fought back with a hail of stones.

Two Spaniards and a German were jailed for up to 10 months for violence around the summit at the weekend. Activists said they had called off a major demonstration planned for Thursday after it was banned by German authorities.

But political tensions also emerged inside the security zone over climate change and other key issues.

One of the main points of friction between the leaders of Britain, Canada, France, Germany, Italy, Japan, Russia and the United States was climate change.

Summit host, German Chancellor Angela Merkel, had wanted fellow leaders to agree to limit the global temperature rise to two degrees Celsius (3.6 degrees Fahrenheit) and to cut greenhouse gas emissions by 50 percent compared with 1990 levels by 2050.

But the United States refuses to sign up to any sort agreement that entails concrete targets.

Merkel put on a brave face when appearing for cameras before the summit dinner and insisted the atmosphere in Heiligendamm was "constructive."

"Many parties have taken some steps forward," she told German television, while conceding there was immediate consensus on climate change.

Bush, too, was keen to appear conciliatory.

"I come with a strong desire to work with you on a post-Kyoto agreement and about how we can achieve major objectives," the US president said after a bilateral meeting with Merkel.

"One of those of course is the reduction of greenhouse gases, another is becoming more energy independent, in our case from crude oil."

Bush spoke after a top aide, Jim Connaughton, chairman of the US government's Council on Environmental Quality, said all key polluting nations had to be involved in any deal.

"We've not sat down with China, India, Brazil, Mexico, South Africa," Connaughton said.

"We have not sat down with Australia, South Korea and a number of the other major emitting countries on this issue and so until we've got everyone in the room and until we have consensus among all of them you won't see a collectively stated goal on that yet, but it's coming."

Merkel's chief environmental advisor, Hans Joachim Schnellnhuber, said the German hosts would be content with any reasonable and concrete benchmark that all the member states could support.

The summit atmosphere had also been soured by tensions between the US and Russia over a missile defence system that Bush's administration wants to establish in central Europe.

Bush, who will hold talks with Russian President Vladimir Putin on Thursday, accused Russia of letting reforms slip before arriving in Germany.

The Kremlin rejected Bush's accusations, insisting that Russia is "a democratic country."

Moscow describes the US missile shield as an aggressive step which would threaten its security. Putin has threatened to turn his missiles on European targets if it is built, and US offers to open up the system to Russian inspections have failed to ease Moscow's anger.

But again Bush sought to ease the tensions. Russia is not a threat he told reporters Wednesday. "Russia is not going to attack Europe."

The US president also held talks with Japan's Prime Minister Shinzo Abe, making his G8 debut, and the two agreed on the need for the G8 final declaration to take a tough line on North Korea's nuclear weapons.

Chinese President Hu Jintao and counterparts from five emerging economies -- Brazil, China, India, Mexico and South Africa -- will participate in some sessions of the summit, highlighting their growing weight in international affairs.

British Prime Minister Tony Blair has said he would use his last G8 summit before leaving office to urge fellow leaders to make good on pledges to help Africa and the world's poor that were agreed at the 2005 G8 summit in Scotland.

The summit will also be the last one for Russia's Putin while newly-elected French President Nicolas Sarkozy is another making his first appearance.