The U.S. government on Friday welcomed the first debate between the two Egyptian presidential frontrunners but urged them to respect the existing peace treaty between Egypt and Israel.

"I think it's a good and healthy thing that they're having a debate," State Department spokeswoman Victoria Nuland said in the wake of the first Egyptian presidential debate between Amr Moussa and Abu El Fatouh, two forerunners in the presidential race.

"But we've made no secret of our hope and expectation -- that whomever is elected -- that the Egyptian political system going forward will honor existing obligations and have peaceful relations with its neighbors," she told reporters at a briefing, apparently referring to the 1979 Egypt-Israel Peace Treaty signed by then Egyptian President Anwar El Sadat and Israeli Prime Minister Menachem Begin.

The debate, aired live on television on Thursday evening, was the first of its kind in Egyptian history. Fatouh was the former member of the Muslim Brotherhood. Moussa was Egypt's foreign minister from 1991 and 2001 and then served as secretary general of the Cairo-based Arab League from 2001 to 2011.

Both agreed, in the debate, to review the relations with Israel, which have seen turbulences since last year, especially after Egyptian protesters stormed the Israeli embassy in Cairo. Fatouh went further by saying that Israel is an enemy.

Their remarks triggered concerns over the prospect of the Egypt- Israel Peace Treaty, which is critical for the security of the Jewish state and the peace in the Middle East.

"We want to see free, fair, transparent elections, and we want to see whomever is elected represent the best interests of all Egyptians, the human rights, democracy, constitutional rights of all Egyptians," Nuland said.

According to polls, Moussa and Fatouh have been the top two popular candidates, among the total of 13.

The presidential vote is set to be held on May 23 and May 24. A run-off will be held in mid June if no one wins in the first round.