Countries worldwide have appealed for calm after days of unrest spiralled into retaliatory attacks by Israel and Palestinians.
The US, the European Union and the UK have urged Israel and the Palestinians to lower tensions as soon as possible.
The violence escalated on Monday night after Palestinian militants fired rockets toward Jerusalem.
In response, the Israeli military launched air strikes against militant targets in the Gaza Strip.
Palestinian health officials in Gaza said 20 people, including children, had died in the strikes. Israel's military said at least three members of the Hamas group that rules Gaza were among those killed.
Hamas had threatened to strike after hundreds of Palestinians were injured in clashes with Israeli police at a holy site in Jerusalem on Monday.