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The United Nations housing organization, U.N.-Habitat, is calling for global improvements in urban planning, as cities around the world mark World Habitat Day.

The official kick-off for the global commemoration was being held Monday at the U.S. National Building Museum in Washington. The opening ceremonies featured a video address by U.S. President Barack Obama.

In a statement, U.N. Secretary-General Ban Ki-moon said meeting the needs of city-dwellers in a rapidly urbanizing world is urgent.  He said evidence from around the world suggests that governments at all levels are largely failing to address the challenges of global housing needs.

U.N.-Habitat officials picked this year's theme, "Planning Our Urban Future," to raise awareness of the need to improve urban planning to deal with the new major challenges of the 21st century. 

The agency says in many parts of the world urban planning systems have changed very little and are often contributors to urban problems, instead of improving the environment.

The United Nations declared the first Monday in October as World Habitat Day, and it has been celebrated annually since 1986.  It says the purpose of the day is to reflect on the state of towns and cities and the basic right of all humans to adequate shelter. 

The day is intended to remind the world of its collective responsibility for the future of the human habitat.

The U.N. Special Rapporteur on the right to adequate housing, Raquel Rolnik, says that some one billion people worldwide live in overcrowded conditions or slums and information urban settlements.