WASHINGTON (AP) — President Barack Obama paid tribute Tuesday to the nearly 200 citizens of the Netherlands who died when a Malaysia Airlines flight was shot down in Ukraine, visiting the Netherlands Embassy in Washington and pledging unity during a phone call with the Dutch leader.

At the embassy, Obama said he wanted to assure the Dutch people that the U.S. will work with them to recover the bodies of their loved ones, to ensure a proper investigation and to bring those responsible to justice.

Adding his inscription to a condolence book, Obama said the sorrow Americans feel over the tragedy is made even more acute by the deep ties between the U.S. and the Netherlands.

"Bound by that friendship, we will not rest until we are certain that justice is done," Obama wrote.

Out of the 298 passengers and crew killed on the flight bound for Malaysia from Amsterdam, the Netherlands was the hardest hit nation, losing 193 citizens.

In a phone call later, Obama and Prime Minister Mark Rutte discussed concerns that Russia was continuing to send weapons and fighters into Ukraine to support pro-Russian separatists, the White House said. The U.S. has accused those separatists of launching the missile that brought down the plane.