Terrorism, while not on the agenda, forced its way into the meeting "in a most tragic and hideous fashion, and produced a united reaction of condemnation and resolve," he said in a statement released in New York.

"This highlights once again the importance of agreeing, in September, on a common definition of terrorism, so that all nations can agree what it is that they are fighting," he said.

Annan has been pressing the 191 U.N. member states to use a world summit in New York in September to reach quick agreement on the text of a new blanket treaty against terrorism, which has been stalled for years in the General Assembly.

The dispute has centered on what constitutes a terrorist act and in particular how to classify Palestinian suicide bombings and Israeli military actions in the West Bank and Gaza, with some nations arguing that one country's terrorist was another's freedom fighter.

The U.N. leader, who was in Gleneagles during the summit, praised the leaders' vow to raise annual development aid for Africa to $50 billion over five years -- doubling 2004 levels -- and cancel the foreign debts of 18 of the poorest nations.

But he lamented there had been no deal to eliminate trade barriers erected by rich nations to poor countries' farm exports. "They will have another opportunity to do so in December, at the World Trade Organization meeting in Hong Kong," he said.

Annan praised the Gleneagles action plan on climate change as "an important step forward" but said he now wanted governments to agree on a global framework for stabilizing greenhouse gas emissions beyond 2012, a step that US President George W. Bush has been resisting.