Fifty international aid groups and U.N. agencies on Thursday urged Israel to open Gaza's borders, saying its border blockade violates international law and indiscriminately harms Gaza's 1.6 million people.

The appeal was issued on the fifth anniversary of the imposition of the blockade, triggered by the violent takeover of Gaza by the Islamic militant Hamas in June 2007. Two years ago, Israel started allowing imports of most consumer goods, but continues to ban virtually all Gaza exports and travel through Israeli crossings.

Israel has said the blockade is meant to prevent Hamas from building up its military arsenal and Gaza militants from carrying out attacks on Israel. The Hamas founding charter calls for the destruction of Israel, and over its 25-year history, the group has killed hundreds of Israelis in shootings and bombings.

However, international aid agencies say the blockade mainly punishes ordinary Gazans by crippling the territory's economy, forcing foreign donors to spend money on humanitarian relief instead of investing in the economy.