U.S. President Barack Obama gestures during a joint news conference with British Prime Minister Gordon Brown in London on Wednesday. (Phil Noble/Associated Press)

Downplaying a possible rift ahead of Thursday's G20 summit, U.S. President Barack Obama exuded optimism Wednesday, saying he was confident member countires would find common ground in efforts to overcome the global economic crisis.

During a joint press conference with British Prime Minister Gordon Brown ahead of G20 talks in London, Obama vowed that the U.S. is doing all it can to revive its own economy and is anxious to work with other countries.

Obama acknowledged that the G20 leaders are not likely to agree on every point. "Having said that, we must not miss an opportunity to lead, to confront a crisis that knows no borders," he said.

The president disputed criticism that the United States is feuding with other nations about the need to pump more money into economic stimulus policies, saying any differences are "vastly overstated."

"I am absolutely confident that this meeting will reflect enormous consensus about the need to work in concert to deal with these problems," Obama said.

Obama is prodding nations to spur economic growth and work together on regulatory reform. The world cannot fall into the kind of protectionism that helped fuel the Great Depression, the president said.

All nations have a "responsibility to act with a sense of urgency," Obama said. "We can only meet this challenge together."

Harper 'optimistic' ahead of meetings

In an interview with CBC News in London on Wednesday, Prime Minister Stephen Harper echoed Obama's call for co-operation and said he was "optimistic" heading into the G20 meetings.

"We're virtually all in the same boat here. There are geopolitical rivalries, obviously, among some of the players around the table on other matters.

"But to the extent that we are — most of us — now all part of a genuinely global economic system and global trading arrangement we should all view ourselves as solutions to a global problem," he said.

He later attended a reception at Buckingham Palace with other G20 leaders, hosted by the Queen.

Following the royal reception, the leaders met for a working dinner Wednesday night. Summit meetings continue Thursday.

Regulation a bone of contention

Harper has talked about the need for world economies to regulate their financial systems, but has steered clear of advocating for an international regulatory body, as suggested by some European leaders, particularly by French President Nicolas Sarkozy.

"But this could turn out to be one of the flashpoints of the meeting here this evening and tomorrow," said the CBC's Keith Boag, reporting from London. "The european countries are very much putting a blame for a lot of what has happened on the United States and Wall Street, precisely for lacking in regulatory controls.

"So there's more enthusiasm for peer review and perhaps international oversight of those things than Stephen Harper would be comfortable with."

Sarkozy, who has threatened to walk out of the summit unless the group agrees on strict financial regulations, was the last to arrive at the G20 dinner.

Sarkozy has said that he would rather risk a public dispute than accept a vague consensus or a "false compromise."

German Chancellor Angela Merkel, who spoke with Sarkozy late Tuesday evening, has also said that leaders "should not dodge and make feeble compromises on the financial market constitution of the future."

A series of one-on-one talks among the 19 countries attending the summit — the European Union takes the 20th spot — are also scheduled.

Heading into the meetings, leaders have tried to focus on the limited common ground they could reach, including more money for the International Monetary Fund and closer scrutiny of hedge funds and tax havens.

There is also growing consensus on the need to address the plight of developing countries, amid growing fears that the heavy toll exacted by the global economic crisis on those nations could come with heavy human and political costs.

Thousands protest

Meanwhile, thousands of protesters converged on central London to rally against the summit, which has been dubbed "Financial Fool's Day."

Obama acknowledged the impact of the economic crisis on citizens who have lost their jobs and homes, but still encouraged consumers to spend.

"Basing decisions around fear is not the right way to go," Obama said. "We are going to get through this difficult time."

The press conference was held after Brown and several of his cabinet ministers had met with Obama in private.

The president said systems in Europe and elsewhere in the world have also struggled, but added he is less interested in identifying blame than fixing the current problems.

Brown agreed the problem requires a global solution.

The discussions at the G20 economic crisis summit will likely be tough, Brown said.

"The world does want to come together," he said.

With files from the Associated Press