The Russians, the Syrians, and the Iranians all pointed the finger at Israel for carrying out a strike on a Syrian military base near Homs.
Israel has not commented, but a former commander of the Israeli Air Force has said it was almost certainly Israel that carried out the strike.
Monday's incident is a reminder that proxy wars continue in Syria amid the seven-year conflict's shifting sands.
Here's what you need to know:
The strikes come just two days after a suspected chemical attack in Douma, the last rebel-held town in Eastern Ghouta, on the outskirts of the Syrian capital, Damascus.
Several world leaders, including US President Donald Trump, blamed Syrian President Bashar al-Assad's government for carrying out the attack. Syria has denied involvement and accused rebels of fabricating the chemical attack claims.
Former Israel Air Force Commander Maj. Gen. Eitan Ben Eliyahu said the alleged use of chemical weapons "could not have gone without a response."
But the suspected use of chemical weapons may also have provided a timely pretext for a far more pressing matter for Israel: the growing presence of Iran in Syria.
Israel has repeatedly expressed its red lines when it comes to Syria. It will not allow the transfer of high-powered weapons to Hezbollah; it will not allow any breach of Israeli sovereignty; and, as apparently in this case, it will work to prevent Iran from entrenching itself in Syria.
The base that was struck, known as T-4, has an Iranian presence, which Iran confirmed when the semi-official Fars News Agency said four Iranians had been killed in the strike. In addition, Israel says an Iranian drone that penetrated Israeli airspace in February was launched and controlled from this base.
Speaking to Israeli Army Radio, leader of the opposition Yesh Atid party, Yair Lapid, said: "T-4, which is the base we're talking about, is no longer just a Syrian base, it is a Syrian-Iranian base. And Israel has said -- and we are clear on this -- that Israel will not accept an Iranian military presence in Syria, and will not accept (Iran's) creeping presence in Syria. This has a price."
Why is Iran such a concern?
Israel considers Iran an existential threat and the biggest danger to the future of the country. Israel watches Iran's growing influence in the Middle East -- from Iraq to Syria to Lebanon -- with a sense of alarm, urging Russia, the United States, and others to take action. But Israel has largely relied on itself to attempt to curb Iran's presence in Syria.
Before the Syrian civil war broke out in 2011, Israel had reached an unspoken understanding with Syria that allowed the two neighboring countries to co-exist, even though Syria has never recognized the state of Israel.
But Iran's presence in Syria changed that tacit status quo, and Israel has carried out numerous strikes on the country in recent years.
Iran has threatened to destroy Israel, with hardline demonstrators chanting "Death to America" and "Death to Israel" in protests.
The Iran nuclear deal, which Israeli Prime Minister Benjamin Netanyahu stringently opposed, has only added to Israel's concern, lifting sanctions against Iran while allowing it to develop ballistic missiles and continue nuclear research.
What about Trump's comments that he might pull US troops from Syria?
US President Donald Trump's announcement that he was considering pulling troops out of Syria worried Israel, but under Netanyahu, the Israeli government is unlikely to openly criticize the US position.
From Israel's perspective, the US presence in Syria is at least a tiny foothold against Iran and a measure of leverage over the future of the war-torn country. Losing that would be a blow to Israel's efforts to keep Iran as far away from Israel's borders as possible.
As Public Security Minister Gilad Erdan said on Israel Army Radio on Sunday: "We hope that the American presence and the international presence (in Syria) will increase, otherwise the genocide is only going to worsen."
Why is Russia so important in all of this?
Russia and Israel have generally sought to coordinate military action over Syria, in the interests of deconfliction. The coordination mechanism was put in place after Russian forces entered Syria in 2015, and Netanyahu has made it a priority in his meetings with Russian President Vladimir Putin.
Previously, Israel has notified Russia of its actions in real time, but this time, a spokesman for Putin said there was no contact between Israel and Russia before or during the overnight airstrike in Syria. Dmitry Peskov, speaking on a daily call with media, when asked whether any such communication had taken place, said, "There were no contacts between Putin and his Israeli counterparts."
That would be incredibly unusual, since maintaining good relations with Russia is key if Israel wants to keep operating in Syria.
Peskov added that Putin intends to speak with Netanyahu about the strike, since Russian advisers were still at the base.
"Of course, this is the cause for our concern," Peskov said. "The communication with the Israeli side is going via the according channels."
The coordination mechanism has begun to show signs of strain in recent months. In February, when Russia moved its SU-57 stealth fighter jets into Syria, a Russian politician appeared to be referring to Israel when he said the presence of the fighter jets was sending a political message "to aircraft from neighboring states which periodically fly into Syrian airspace uninvited."
- Why would Israel launch strikes on Syria?
- Iran vows to retaliate against Israel for Syria strike
- After Syria strikes, now what?
- US steps up surveillance of Iranian assets in Syria over concerns of strike against Israel
- What we know about the Syria strikes
- Trump declares 'mission accomplished' in Syria strike
- US, UK and France launch Syria strikes targeting Assad's chemical weapons
- Israel claims 82,000 fighters are under Iranian control in Syria
- Israel behind airstrike in Syria, US official says
- Israel helps evacuate Syria's White Helmets to Jordan