The Fourth Geneva Convention, specifically Article 49(6), prohibits the transfer of an occupying power's civilian population into occupied territory. This is the primary legal basis for the argument that settlements are illegal.
UN Condemnation:
The UN Security Council and General Assembly have repeatedly passed resolutions condemning Israeli settlements, calling for their cessation and dismantling. UN Security Council Resolution 2334, for example, reaffirmed that Israeli settlements in the West Bank have "no legal validity" and "constitute a flagrant violation of international law," UN Press Releases.
ICJ Opinion:
The International Court of Justice (ICJ) has also issued advisory opinions finding that Israeli settlements are illegal under international law. The ICJ has called on Israel to cease settlement activities and evacuate settlers.
Israeli Perspective:
Israel maintains that the settlements are legal, citing historical and religious ties to the land and the right to self-determination. However, these arguments are not recognized by the international community, which views the land as occupied territory.
Israeli Law:
While Israeli law permits settlements in the West Bank, it is not recognized as legal under international law. Israeli settlements are built on land that is considered Palestinian territory under international law.