Violence in the Gaza Strip erupted this week with mobs fighting in the streets and rockets flying overhead, prompting serious concern from the international community.
The United Nations Middle East Envoy, Tor Wennesland, told the Security Council that it is "the most serious escalation between Israel and Palestinian militants in years" and warned on Twitter that "we're escalating towards a full scale war."
U.N. spokesman Stephane Dujarric told reporters that the "indiscriminate launching of rockets and mortars from highly populated civilian neighborhoods towards civilian population centers violates international humanitarian law."
Hamas, the terror group that rules the Palestinian territories, has launched hundreds of rockets at Israel over the last two days, including Jerusalem and Tel Aviv. Israel's Iron Dome missile defense system intercepted most of the rockets.
Israel responded with a barrage of airstrikes, taking out Hamas’ Gaza City commander, Bassem Issa, as well as several other senior Hamas militants.
"Israel has a right to defend itself when you have thousands of rockets flying into your territory," Biden told reporters Wednesday.
"My national security staff and defense staff has been in constant contact with their counterparts in the Middle East, not just with the Israelis but also with everyone from the Egyptians to the Saudis to the Emiratis."
U.S. Secretary of State Antony Blinken said he is sending an envoy to the Middle East immediately.
"I think Israel has an extra burden in trying to do everything it possibly can to avoid civilian casualties even as it is rightfully responding in defense of its people," Blinken said Wednesday.
Four UN Security Council members – France, Estonia, Ireland and Norway – issued a statement after a meeting Wednesday calling on both sides "to de-escalate tensions, end violence and show the utmost restraint."
Russian Foreign Minister Sergei Lavrov called on an emergency meeting of four international mediators to try to resolve the conflict.
"I think we came to a common conclusion that the most urgent task is calling a meeting of the quartet of international mediators: Russia, the United States, the UN and the European Union," Lavrov said at a joint briefing with United Nations Secretary-General Antonio Guterres.
UK Prime Minister Boris Johnson urged the two sides to "step back from the brink."
"The UK is deeply concerned by the growing violence and civilian casualties and we want to see an urgent de-escalation of tensions," he wrote on Twitter.
At least 56 people have been killed in Gaza since violence broke out on Monday, while six people have been killed in Israel.
Israeli Prime Minister Benjamin Netanyahu deployed Border Police forces Wednesday, saying that Israel will "stop the anarchy and restore governance to the cities of Israel, with an iron fist if needed, with all forces needed and all authorities required."
The Associated Press and Reuters contributed to this report.