Senate Foreign Relations Chairman John Kerry (D-Mass.) said Sunday that the United States must take an active role in working to ease the tension in the Middle East following Israel’s deadly raid of a flotilla headed for the Palestinian territories in the Gaza Strip.

Israel has “every right” to take action to ensure weapons are not being smuggled into Gaza, Kerry said during an appearance on ABC’s “This Week.” But shipping humanitarian supplies to Gaza remains important, so more clarity is needed on what items can go through Israel’s blockade, he added.

“What we need to do in the days ahead is put out a list of things that cannot go in, and have clarity for those groups trying to get things in,” Kerry said.

If the response to the crisis is not swift, countries such as Iran could use it to their advantage, he said.

“There’s nothing they would like more than to create a violent explosion, and the tension is real enough that there is the threat of war in the Middle East,” Kerry said. “We need to work extra hard in these next few days to bring the parties together.”

U.N. Secretary General Ban Ki-moon recently called for an international investigation of Israel’s raid, which resulted in the deaths of nine people, including a U.S. citizen. But that idea was dismissed Sunday by Israel’s ambassador to the United States, Michael Oren, who said on “Fox News Sunday” that his nation “will do whatever it takes to defend itself from Hamas terror.” Hamas is a Palestinian Islamic political party with an armed wing by the same name.

“Israel has the ability and the right to investigate itself,” Oren said. “We are rejecting the idea of an international commission.”

Oren added that Israel’s “relationship with the Obama administration throughout this episode has been very close.”

Republican Sen. John Cornyn (Texas), who also made an appearance on “This Week,” said Israel has the right to take action to see if weapons are being brought in.

“This was pretty clearly a pre-meditated provocation, and it’s unfortunate that lives were lost,” Cornyn said.