Leaders of the world's top industrial and developing countries are starting to arrive in the eastern U.S. city of Pittsburgh for a summit on the world's financial future.  Ahead of the meeting Germany is warning them not to lose their focus.

German Chancellor Angela Merkel says the top priority for the Group of 20 summit must be regulating financial markets that allowed risky behavior to plunge the world into a deep recession.

Ms. Merkel spoke in Berlin before leaving for the summit that starts Thursday, hosted by U.S. President Barack Obama.

Her comments reflect tensions among world leaders on the best ways to help make sure the events that caused the global financial crisis are not repeated.

Disagreements remain over when countries should begin to roll back stimulus measures and over how much control the international community should have over financial markets within individual countries.

Leaders are also expected to work on ways to promote global trade, repair lending systems and provide financial support to developing countries dealing with climate change issues.

Several bi-lateral meetings are also scheduled before the summit officially gets underway, including talks between U.S. Treasury Secretary Timothy Geithner and Japanese and Chinese officials.

Members of the G20 include the United States, Brazil, China, Indonesia, Mexico, France, and Germany.

The rest of the members are the European Union, Argentina, Australia, Britain, Canada, India, Italy, Japan, Russia, Saudi Arabia, South Africa, South Korea, and Turkey.

Some information for this report was provided by AP and Reuters.