WASHINGTON (BLOOMBERG) - United States President Donald Trump made a direct flight on Monday (May 22) between two nations that have historically been sworn enemies, Saudi Arabia and Israel - a first for Air Force One.

Mr Trump travelled from Riyadh to Tel Aviv in what appears to be an unprecedented direct flight by a US president between those nations, which don't have diplomatic relations, in a region fraught with tension.

"It's a direct flight," Secretary of State Rex Tillerson told reporters travelling with the president aboard Air Force One.

Of hopes for a peace plan between Israel and the Palestinians, Mr Tillerson added, "There's a moment in time here."

Speculation of such a flight by Mr Trump into Israel from the Saudi capital has swirled for weeks. The Haaretz newspaper noted that two past sitting US presidents - Richard Nixon and Bill Clinton - had previously flown from Syria into Israel, but none had made the flight directly from Saudi Arabia.

On the eve of Mr Trump's departure, it wasn't clear if the flight would indeed proceed without any stops - although the President's schedule shows such a route, lasting slightly under three hours.

While there may have been similar flights in the past by US diplomats conducted below the radar, a very public direct flight could cross an important threshold with implications for the region's politics and economics.

"The symbolism is interesting," said Mr R. Nicholas Burns, a diplomacy and international relations professor at the Harvard Kennedy School of Government who served at the State Department. "What is happening behind the scenes over the past few years is that the Israelis probably have better contacts with the Gulf Arabs than they've ever had before."

In recent years, fears of an ascendant Iran have begun to chip away at differences between Arab countries and Israel over the Palestinians. Trade and collaboration in technology and intelligence are flourishing between Israel and a host of Arab states.

Still, those contacts are largely kept quiet, and travel connections are limited. There aren't many direct flights into Tel Aviv from the Middle East region; Jordan's proximity and warmer relations with Israel allow a way in.

There are no bilateral agreements allowing air-traffic controllers from many Arab nations to interact with their Israel counterparts, according to two people familiar with the situation, who asked not to be named because of the political sensitivities in the region.

Because of that and other restrictions, Israeli aircraft aren't permitted to fly over most of its Arab neighbours.

Even flights between Europe and hubs such as Amman or Dubai go hundreds of kilometres out of their way to avoid Israeli airspace, according to flight tracking website FlightRadar24.

Israel has long sought the right to fly over Saudi Arabia as one of the possible fruits of peace with the Arab world, said Mr Yiftach Shapir, a senior research fellow at the Institute for National Security Studies in Tel Aviv.

Flying between Tel Aviv and Mumbai, for example, would take less than five hours if El Al Israel Airlines could take a direct path. Instead, it takes about eight hours as planes are routed over the Red Sea to avoid the kingdom, before flying east over the Horn of Africa and across the Arabian Sea to reach India.

"It's a ridiculously circuitous route," Mr Shapir said. "Getting overflight rights would save a lot of time and money, not just for El Al, but also for other airlines that fly to Israel and are subject to the same rules."

Haaretz reported, citing unnamed government officials, that the upcoming Trump flight might be the first time a plane from Saudi Arabia is permitted to fly directly to the Jewish state. The officials couched the assertion by saying it will be the first "in broad daylight", according to the newspaper.

Not everyone in Israel was impressed. Mr Joshua Teitelbaum, a senior research associate at Bar Ilan University's Begin-Sadat Centre for Strategic Studies, noted that US officials often fly between countries that don't have diplomatic relations, such as former Secretary of State Henry Kissinger shuttling between Israel and Egypt, and Israel and Syria, in the 1970s.

"I don't think what the President is doing now is all that significant," Mr Teitelbaum said. "What will be significant will be if Trump could announce a significant upgrading of relations between Israel and some of the Gulf counties like Saudi Arabia and the UAE. The narrative being advanced by Saudi Arabia and Israel has heightened such expectations."

In the world of high-level diplomacy, in any case, there are usually workarounds to travel restrictions.

Former Middle East envoy Dennis Ross recalled flying on an attaché plane to Israel from Saudi Arabia after Yitzhak Rabin became Israel's prime minister. But even with government flights, there often would be at least a pretense of making a stop in between, he said.

"There would be sensitivities where, rather than make it into a political issue, in the past, they wouldn't fly a direct route. If you were coming out of Saudi Arabia, you could check in with the Jordanian air traffic controllers."

Mr Burns, who was stationed in Israel and also served on teams attempting shuttle diplomacy in the region, said regular people in Israel and its close neighbours in the Middle East were largely excluded from the kind of travel that's routine in much of the rest of the world.

In 1995, Mr Burns was on a team led by then Secretary of State Warren Christopher that was trying to negotiate a peace deal between Israel and Syria.

"In one week, we flew every day - it must have been seven or eight days - between Jerusalem and Damascus," Burns said. The cities are about 217km apart, roughly the distance from Washington to Philadelphia.

"It took no time to get there. But we were the only ones who could fly that route. No Israeli and no Syrian could fly that route."