Qatar and the United States are on the verge of finalizing an enhanced defense cooperation agreement, said top U.S. diplomat Marco Rubio who was on his way to Doha from Tel Aviv on Tuesday after Israel's attack on Hamas political leaders in Qatar last week drew widespread condemnation.

Israeli Prime Minister Benjamin said he did not did not rule out further strikes on Hamas leaders "wherever they are," as the heads of Arab and Islamic states held a summit to back Qatar after Israel's attack last week in the Gulf state.

Rubio called for Qatar to continue its role as a mediator between Israel and Hamas to reach a ceasefire in the Gaza war, saying there was "a very short window of time in which a deal could happen."

"If any country in the world can help mediate it, Qatar is the one. They're the ones that can do it," Rubio said while departing Tel Aviv for Doha.

Qatar called the Israeli attack "cowardly and treacherous," but said it wouldn't deter it from its role as a mediator, alongside Egypt and the United States.

"We have a close partnership with the Qataris. In fact, we have an enhanced defense cooperation agreement, which we've been working on, we're on the verge of finalizing," Rubio said.