WASHINGTON — President Barack Obama is expressing serious concern about the rising number of casualties in the Gaza Strip.

Obama on Monday called for an immediate cease-fire. He’s asking Secretary of State John Kerry to do whatever he can to help negotiate one at talks in Egypt.

Israel’s fight against Hamas has killed at least 530 Palestinians and 20 Israelis and displaced tens of thousands of people from Gaza in the past two weeks.

The president says Israel has already done significant damage to Hamas. But he says he doesn’t want to see more civilians getting killed.

In comments made Wednesday morning at the White House, the president also addressed the continuing lack of access to the site where a Mayalasia Airlines crash in the Ukraine. site for international investigators.

Obama accused pro-Russian separatists in the area of removing evidence and bodies from the crash site. He said that activity raised the question of “what exactly are they trying to hide?”

The president says the burden is on Russia and President Vladimir Putin to compel the separatists to cooperate with the investigation. Obama says that if Russia continues to violate Ukraine’s sovereignty, Moscow “will only further isolate itself” and the economic costs will continue to increase.

The White House says the missile that brought down the Malaysia Airlines plane was fired from an area controlled by the separatists.