Soaring global food prices could unleash a “silent tsunami” that would plunge 100 million people who previously did not require help to buy food into hunger and poverty, the top United Nations food official said at a conference on the growing crisis in London. “This is the new face of hunger,” the official, Josette Sheeran, the executive director of the World Food Program, added. “The response calls for large-scale, high-level action by the global community.” She was one of 25 experts in the field who attended the conference hosted by Prime Minister Gordon Brown at his Downing Street office. Prices for basic foods like rice and wheat have risen rapidly since the last quarter of 2007, leading to riots and protests in a number of countries. In the latest unrest, demonstrators took to the streets in the Afghan city of Jalalabad and the Gabonese capital, Libreville. A statement from Mr. Brown’s office released after the meeting said that delegates had pledged to work with the G-8 and European Union toward a global strategy to tackle price rises and increase support for the world’s poorest nations. There was also agreement for a “more selective approach” to biofuels, cited by some for causing the food price surge.