Israel's parliament has given preliminary approval to a piece of legislation that would require a national referendum on any peace deal that gives up control of east Jerusalem or the Golan Heights.

If approved, the law could constrain the ability of any future Israeli government to turn over captured land as part of a peace deal.

The Palestinians seek east Jerusalem as the capital of a future state, while Syria has demanded the return of the Golan Heights as part of any peace agreement with Israel.

Israel captured both areas in the 1967 Mideast war and subsequently annexed them.

The measure was approved by parliament 68 to 22 on Wednesday. It still needs to pass two more parliamentary votes to become law.