HEILIGENDAMM - The United States said on Wednesday it opposed setting firm targets for greenhouse gas cuts at a G8 summit but offered reassurance that its plan for fighting climate change would not undermine UN efforts.

US President George W. Bush meets with Chancellor of Germany Angela Merkel at the G8 summit in Heiligendamm, Germany, June 6, 2007. [Reuters]

US President George W. Bush's stance prompted hard bargaining at the June 6-8 meeting where German Chancellor Angela Merkel hopes to win a commitment from major powers to halve greenhouse gas emissions by the middle of the century.

Police turned water cannon on protesters near the summit venue on the Baltic coast as world leaders gathered for talks also likely to tackle missile defence and aid for Africa.

Bush told reporters that Russia did not pose a threat to Europe despite a vow by Moscow to target the continent if the US deploys a missile shield in central Europe.

"Russia is not going to attack Europe," Bush said.

Summit host Merkel has been pushing for cuts of 50 percent in greenhouse gases by 2050 to curb a rise in temperatures that scientists say could cause more droughts, heatwaves, floods and rising seas.

But Washington said it was not ready to sign up to such fixed goals in Heiligendamm where Bush will meet leaders of Japan, Russia, Germany, Britain, France, Italy and Canada.

"At this point in time we are not prepared to adopt that proposal," said James Connaughton, a senior White House adviser, when asked about Merkel's emissions target.

French President Nicolas Sarkozy suggested Europeans would press Washington until the very end on the divisive issue.

"We need quantifiable targets in the final text," Sarkozy told reporters. "It is an extremely important point and I intend to talk to the president of the United States about it as early as this evening," he added.

It appeared the United States could accept language calling for "substantial" reductions in global emissions in the long term, according to a draft G8 document written in late May.

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Bush said his plan announced last week for talks among the top 15 emitters of greenhouse gases with the aim of agreeing long-term reductions by the end of 2008 would "fold into the UN framework" on tackling climate change.

Many European nations had expressed concerns that Bush's plan might undermine UN talks on a global deal to replace the Kyoto Protocol, the main UN plan until 2012 for curbing greenhouse gases released mainly by burning fossil fuels.

The United States is the only G8 nation outside Kyoto.

"I also come with a strong desire to work with you on a post-Kyoto agreement about how we can achieve major objectives" including cuts in greenhouse gases, Bush told Merkel after a lunch of veal schnitzel and asparagus.

Merkel, who brokered an EU deal in March which includes binding cuts in emissions, has also been pushing for a G8 pledge to limit warming of global temperatures to 2 degrees Celsius (3.6 Fahrenheit), seen as a threshold for dangerous changes.

But she may have to settle for an expression of US support for United Nations efforts to combat climate change and an agreement to tackle emissions at a later date.

"I think we all know that the goals agreed by the European Union cannot be accepted by the entire world," she said.

Officials were also involved in last-minute wrangling over commitments to fighting poverty in Africa, another of Merkel's G8 priorities. Leaders will refer to pledges made at the Gleneagles summit in 2005 to double development aid by 2010.

But Italy and Canada are resisting concrete language in the communique on a pledge to lift overall annual aid by $50 billion by 2010 and also, with Japan, blocking country-specific figures.

Near the venue, police used water cannon to disperse groups of protesters and clear roads, detaining some 160 activists. Eight police officers were injured in the clashes.

Some marchers damaged a rail track used to shuttle officials in and out of the summit site. Others blocked roads, temporarily cutting off all ground access to the venue.

"We had a super plan and we surprised the police, who didn't know how to stop us," said Gunar Finke, a student from the southern German city of Freiburg.