The United Nations secretary-general is welcoming the open-ended cease-fire reached by Israel and Hamas in Gaza but warns that "any peace effort that does not tackle the root causes of the crisis will do little more than set the stage for the next cycle of violence."

The statement by the spokesman for Ban Ki-moon on Tuesday said Gaza "must be brought back under one legitimate Palestinian Government," that the blockade of Gaza must stop and that Israel's security concerns must be addressed.

It adds: "After 50 days of profound human suffering and devastating physical destruction, any violations of the cease-fire would be utterly irresponsible."

The U.N. statement stresses that a political process that leads to two states is the only way to reach lasting peace in Gaza.