The new head of the United Nations agency tasked with promoting sustainable cities?Wednesday outlined the challenges facing urban centres around the world, saying they were hosting increasingly large populations but had limited resources for critical services.

Pointing out some of the issues he will be addressing as the Executive Director of the UN Human Settlements Programme (UN-HABITAT), Joan Clos said that although cities hosted industries and businesses that create much of the world's wealth, they were not always able to raise the resources required to deal with the problems associated with expanding population.

"We need to understand better the economic role of urbanization," Mr. Clos said, adding that he will balance "continuity and renewal" during his term as head of the organization.

"We need to produce some changes and improvements in our organization in order to be more focused and more efficient inside the overall objective of the United Nations of delivering-as-one and being more efficient in general," Mr. Clos said.

He stressed that that while cities in the developing world continued to be plagued by problems associated with poverty, underdevelopment, poor health and standard of education and insecurity, new challenges to urban areas in both poor and richer countries were arising.

They included cities as emitters of green house gases that contribute to climate change and the risk of the collapse of transit systems due to inadequate planning and rapid expansion.

UN-HABITAT will be seeking solutions to the new challenges facing urban authorities with a view to helping them as wells as governments in their efforts to seek solutions to them, Mr. Clos said.

Mr. Clos, former mayor of the city of Barcelona in Spain, was appointed as head of the Nairobi-based agency by Secretary-General Ban Ki-moon in August, starting work on 16 October.

He succeeded Anna Tibaijuka, a citizen of Tanzania, who headed UN-HABITAT since it was formed in 2001 to replace the UN Centre for Human Settlements.