United Nations secretary-general Kofi Annan has condemned the deadly bombings that killed at least 33 people and injured more than 340 in London.

He has called them "an attack on humanity itself" and has expressed solidarity with the British Government and people.

"I was devastated by the atrocious bombings that struck London today," the UN chief, who was on his way to the summit of the world's most powerful leaders in Scotland, said in a statement.

"These vicious acts have cut us all to the core, for they are an attack on humanity itself.

"Today the world stands shoulder to shoulder with the British people, who with others around the world had mobilised so powerfully against poverty and climate change ahead of the Group of Eight summit, and who, I am sure, will confront this ordeal with the same spirit, courage and determination," he said.