Katowice, June 28 : Cities are "central to virtually every challenge we face -- and essential to building a more inclusive, sustainable, and resilient future", United Nations (UN) Secretary General Antonio Guterres has said in a video message. Guterres made the remarks during the 11th World Urban Forum (WUF) that opened in Katowicze, southern Poland, on Monday, Xinhua news agency reported. The WUF is the premier global conference on sustainable urbanisation. Cities "have been on the frontlines of the Covid-19 pandemic," he said. "They must also be leaders of climate action to keep the 1.5 degrees Celsius goal within reach." The theme of the 11th WUF, "Transforming our cities for a better urban future," "could not be more fitting," said Maimunah Mohd Sharif, UN under-secretary-general and executive director of the UN Human Settlements Program (UN-Habitat). Participants will also hold a special session on the post-crisis and post-disaster reconstruction of urban spaces and population return. Held every two years, the WUF is convened by UN-Habitat. More than 16,000 people are expected to attend the event this year. /IANS