VIENNA, May 28 (Xinhua) -- The Vienna Energy Forum, an international energy event sponsored by the United Nations and Austria, opened here Tuesday with a focus on promoting the role of sustainable energy in the post-2015 development agenda.

Some 1,500 participants, including government officials, energy experts, and representatives of international and non-governmental organizations, academia, civil society and the private sector attended the three-day international energy event at the Hofburg Palace.

Kandeh K. Yumkella, director general of the UN Industrial Development Organization (UNIDO) said that an achievement of energy sustainability should be an important solution to the future development agenda.

"Energy is now recognized as a defining issue of our time. The lack of access to energy is a crucial constraint for development efforts," Yumkella said.

That is why the post-2015 development agenda will pay great attention to the energy issue, he said.

"Energy is the largest industry, and it is closely related with all industries and production areas. Because of this, UNIDO has been attaching great importance to the promotion of the development of sustainable energy worldwide," he said.

UNIDO is willing to take practical actions to help improve people's lives and social conditions and develop the economy while protecting the environment, he said.

At the forum, many participants said that energy and development are inseparable, and that energy sustainability is the trend of global development.

Many speakers said that the "Sustainable Energy for All" initiative of UN Secretary-General Ban Ki-moon should become a major part of the post-2015 development agenda, and become a goal of global energy development.