The United Nations says six billion of the world’s seven billion people have mobile phones but only 4.5 billion have access to toilets or latrines.

So the UN is launching a global campaign to improve sanitation for the 2.5 billion people who don’t have it.

UN Deputy Secretary-General Jan Eliasson called their plight “a silent disaster” that reflects the extreme poverty and huge inequalities in the world today.

Eliasson told a press conference Thursday that the issue must be addressed immediately for the world to meet the UN goal of halving the proportion of people without access to sanitation by the end of 2015. World leaders set a series of Millennium Development Goals to combat poverty at a summit in 2000, and Eliasson said the sanitation goal lags farthest behind.

While most people don’t want to talk about the problem, Eliasson said, “it goes to the heart of ensuring good health, a clean environment and fundamental dignity for billions of people.”

The UN said action must include eliminating by 2025 the practice of open defecation, which perpetuates disease.