UN Secretary General Kofi Annan has urged world leaders to agree on a universal definition of terrorism.
More than 60 people were killed in bomb blasts in Egypt on Saturday
The bomb attacks in London and Egypt underscored the need for a definition with "moral clarity" and a UN convention against terrorism, he said.
A UN treaty has been stalled for years over the definition of a terrorist.
A new UN proposal calls terrorism any act intended to intimidate a population or to compel a government or an international body to act.
"The targeting and deliberate killing of civilians and non-combatants cannot be justified or legitimised by any cause or grievance," it adds.
Mr Annan wants the proposed UN terrorism convention to be agreed on by world leaders in time for a UN world summit in September.
"A simple, clear statement bringing in moral clarity that maiming and killing of civilians is unacceptable regardless of one's cause I think will satisfy all of us," he added.
The proposed convention has been stuck in a committee since 1996. The debate has focused on the Palestinian-Israeli conflict.
Arab League Secretary General Amr Moussa backed Mr Annan's latest definition, telling Reuters news agency that it could serve as the "basis for consensus".
However, "resisting occupation is a different issue altogether", he said.
Mr Annan's chief of staff, Mark Malloch Brown, told the BBC that the UN was mindful of objections to the definition on the basis that people who take up arms against a state to protect their freedoms do not have equal rights to strike back.
The UN needed to be understanding and protective of issues of political freedom and political participation, he said.
However, the behaviour of states was already heavily circumscribed by conventions governing the use of force, such as the Geneva conventions, he added.
"The argument now is that individuals who use violence for political purposes must similarly be constrained by similarly unambiguous definitions, and that there must be clear straightforwardness in condemning them," he said.