PARIS—World leaders converged on Paris on Monday for international climate talks amid an unprecedented security lockdown, two weeks after gunmen and suicide bombers killed 130 people in a string of terror attacks.

Heads of state and government from some 150 countries will speak in turn at a highly secure airport complex north of the city over the next two weeks in an effort to reach a global agreement on limiting emissions.

To get a deal by mid-December, negotiators must overcome differences between rich and poor economies, high polluters and countries already suffering from rising temperatures.

"Never, and I say never, have the stakes of an international meeting been so high, since what is at stake is the future of the planet, the future of life," said French President Franç ois Hollande. "Yet two weeks ago here in Paris, a group of fanatics sowed death in the streets."

One emerging sore spot in the talks is the level of funding that richer countries will provide both to aid the transition of poorer countries to cleaner energy and to finance efforts to stave off the early effects of a changing climate.

Developing countries want their highly industrialized peers that have used large amounts of fossil fuels for a century to mobilize $100 billion a year in climate financing, and some officials have warned they won't support a deal in Paris that doesn't deliver high levels of funding. Any agreement would require the consent of nearly 200 countries.

Shortly ahead of the talks, India slammed an October estimate on how much financing rich countries have provided to poorer economies. The Organization for Economic Cooperation and Development set out guidelines in the report to measure whether rich nations are on track to deliver $100 billion in promised annual financing by 2020.

India said the Paris-based think tank overestimated the amount of actual flows when it said it reached $61.8 billion in 2014. "Methodologies used were inconsistent with the literature and best practice and even 'bent' in ways to find more flows than reality," the Indian finance ministry said in a working paper published Friday.

The OECD shot back, saying the report was a genuine attempt to provide a transparent estimate that avoided double counting based on official submissions by rich countries. "The Indian criticisms of the report are misjudged and inaccurate," said Simon Buckle, head of climate change at the OECD.

As part of the rich countries' attempts to soothe tensions over financing, President Barack Obama and Microsoft co-founder Bill Gates unveiled a multibillion-dollar program Monday to boost green-energy research and development.

Messrs. Obama and Gates will join with other heads of state and investors to detail complementary public and private commitments to clean-energy innovation.

"This fund is meant in part to convince developing countries that major nations are serious about clean-energy technology investment in poorer countries, not simply trying to close their coal plants and inhibit economic development," said Paul Bledsoe, a former Clinton White House aide on climate attending the negotiations.

The 20 countries that have signed on to Mission Innovation include leading carbon-dioxide emitters from developed and developing countries, including China, India, Brazil, Indonesia, Saudi Arabia and France. They are pledging to double their investments in clean-energy research and development during the next five years.

The Paris climate talks are taking place on the outskirts of a city still on edge in the wake of the deadly Paris terror attacks.

After arriving in Paris late Sunday night, President Barack Obama visited the Bataclan concert hall to pay tribute to victims of the attacks. At the makeshift shrine outside the theater where gunmen killed at least 89 people, Mr. Obama stood in silence with Mr. Hollande and the mayor of Paris, Anne Hidalgo. The three leaders each laid a single white rose in front of the building.

France has moved to secure the city, shutting down external access points and some thoroughfares Sunday and Monday. The government canceled protests that had been planned by climate activists calling for countries to do more to curb emissions and keep climate change at bay. But that didn't stop unofficial gatherings.

On Sunday, riot police fired tear gas as they clashed with demonstrators who refused to disperse from Place de la Ré publique, north east of central Paris. Candles and flowers from a memorial to the victims of the Paris attacks were scattered in the confrontation. Police said 174 demonstrators were detained.

"These demonstrations are not authorized," Mr. Hollande said. "It's very regrettable, and even scandalous."

Before the Paris talks began, most of the countries involved submitted their own plans for curbing emissions of greenhouse gases linked to climate change or boosting the share of green energy. An accord clinched in Paris would codify those national plans, part of an original goal to limit global warming to less than 2 degrees Celsius above preindustrial levels.

The current pledges are only likely to limit global warming to about 2.7 degrees, officials say, so the U.S., Europe and other countries want the Paris accord to require countries to renew their emissions targets every five years or so, helping shift the world toward the 2-degree goal over time.

"We are at the foot of a wall built from the sum of our egos, fears and resignation," Mr. Hollande said as he opened the conference. "But this wall is not insurmountable."

Mr. Obama and most other heads of state will leave the talks by Tuesday, but other officials will continue negotiations with the goal of wrapping up an agreement at the ministerial level by the end of next week.

"The aim is to formulate political unity from the start," German Environment Minister Barbara Hendricks said.

Gabriele Steinhauser, Colleen McCain Nelson and Bill Spindle contributed to this article.

Write to William Horobin at William.Horobin@wsj.com and William Mauldin at william.mauldin@wsj.com

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(END) Dow Jones Newswires

November 30, 2015 07:05 ET (12:05 GMT)