Jerusalem (CNN) On a January weekend in 2015, an Israeli missile streaked across the country's northern border into Syria. Among seven people killed were Jihad Mughniyeh, the son of one of Hezbollah's founders, and a senior commander from Iran's Revolutionary Guard Corps.

Hezbollah's response was fierce. Rockets rained down for days on the northern Israeli countryside, with the Iranian proxy exchanging fire with Israeli forces near the border. Hezbollah fired five anti-tank missiles at an Israeli convoy on the border, killing two soldiers. As tensions soared along the border, a Spanish soldier serving as a UN peacekeeper was killed in the crossfire.

The Middle East appeared to be sliding toward another regional war, but it did not happen. Both sides pulled back , choosing not to escalate the situation further. Instead, Israel and Hezbollah returned to the same routine, if tense, state under which the border has existed for years.

Three years later, and tensions are back. In fact, the situation has already deteriorated much further than it had in 2015.

It's no longer Israel confronting Hezbollah in a form of proxy war with Iran. Now, Israel and Iran face each other with Syria as the setting for their rivalry. What was for so long a war of words and covert actions between Israel and Iran risks moving closer to open confrontation.

When an Iranian drone entered Israeli airspace in February , it marked the beginning of a new phase between Israel and Iran -- two adversaries vying for regional positioning. It has become one of the biggest subplots in Syria's seven-year civil war, with the potential to draw in even more actors, including, if the situation escalates enough, Russia and the United States.

Israel shot down the drone and struck the base in Syria, known as T-4, from which it was controlled, losing an F-16 fighter jet to Syrian air defenses in the process.

The exchange made one thing clear: Israel and Iran appear to be on a collision course.

A battle that used to be carried out through proxies -- Israel fighting Hezbollah in Lebanon -- has been replaced by near-direct confrontation.

Another, more recent airstrike on the T-4 military base -- a strike pinned on Israel -- killed at least seven Iranian nationals.

A strike this past weekend that targeted Syrian military positions has all the hallmarks of an Israeli attack, though no one has yet blamed Israel. Airstrikes hit bases near Hama and Aleppo, with the London-based Syrian Observatory for Human Rights saying 26 people were killed in the strike, most of them Iranian militiamen.

Iran denied an attack killed its fighters, according to the state-run Tasnim News Agency.

Nevertheless, Iran sees Israel's strikes in Syria as a violation of international law and Syrian sovereignty. Iran is Syria's biggest ally, supportive of President Bashar al-Assad. Iran has offered military assistance, technology and equipment to Assad as he tries to maintain his own position while fighting Syrian rebels and ISIS.

With the strikes attributed to Israel growing more frequent and more brazen, Iran has vowed to respond.

Hossein Salami, a senior Revolutionary Guard commander, issued a harsh warning during Friday prayers, seen as a key signaling tool for the Iranian regime.

"I say this to the Zionists, we know you very well. You are very vulnerable. You have neither depth nor backing. Your mischief has increased. Listen and be aware any war that might happen, rest assured will bring about your disappearance."

Israel has taken Iran's threat seriously, holding multiple security cabinet meetings in recent weeks to discuss tensions in the north. A CNN reporter in the Golan Heights also witnessed what appeared to be a buildup of tanks, armored personnel carriers, and more in the country's north.

"Iranian retaliation is on its way," says retired Israeli Maj. Gen. Amos Yadlin, the executive director of Tel Aviv University's Institute for National Security Studies in Israel. He notes two conflicting positions over Syria, in "the strategic position and determination of Iran to build advanced military forces in Syria, and the Israeli determination not to let that happen." Neither side has shown a willingness to compromise.

Israel views with growing alarm Iran's presence in Syria, with the country's leaders reiterating Israel's position: It will not allow Iran to establish a military presence in Syria.

While Syria might be suffering the fog of war, elsewhere Israel sees a surprising array of clearsighted neighbors and allies, creating favorable conditions to act.

Israel feels it can rely on unwavering support from the administration of US President Donald Trump, as the American President sees eye-to-eye with Israeli Prime Minister Benjamin Netanyahu on the Iran deal.

In the past two weeks, the head of US Central Command, Gen. Joseph Votel visited Israel, newly confirmed Secretary of State Mike Pompeo met with Netanyahu, Israeli Defense Minister Avigdor Liberman met the US secretary of defense and national security adviser in Washington, and Netanyahu spoke with Trump on the phone.

All of that took place before Netanyahu launched his strongest attack yet on the Iran nuclear deal, in a theatrical prime-time presentation. Standing in front of a screen that was taller than him, Netanyahu accused Iran of decades of lies and deception about the country's nuclear ambitions.

Citing a trove of files apparently taken from Tehran that he says prove Iran tried to mislead the world about its program, Netanyahu asked: "Why would a terrorist regime hide and meticulously catalog its secret nuclear files, if not to use them at a later date? Iran lied about having a nuclear weapons program. Iran continued to preserve and expands its nuclear weapons know-how for future use."

Additionally, the Saudis view Iran just as the Israelis do: a major threat to the region that is the Middle East's primary concern. Meanwhile, Egypt is focused on its own domestic issues and the security of the Sinai Peninsula. In other words, two key regional players who formerly had a tendency, in Israel's eyes, to place too much focus on the Israeli-Palestinian conflict, are looking elsewhere now.

"I know one thing for certain. We will not allow the Iranians to base themselves in Syria and there will be a price for that. We have no other choice," Liberman said recently. "To agree to an Iranian presence in Syria, it's agreeing to the fact that the Iranians will put a noose around your neck."

At a conference in New York this past weekend, Liberman insisted Israel still had liberty to act over Syria, even after it lost a fighter jet earlier this year.

Syria is a fractured country, but even in its shifting sands, Iran and Israel have drawn their red lines.