The United States said Monday it had carried out a strike against Al-Qaeda-linked jihadists in northwestern Syria, its first such operation there in two years.
On another front in Syria's complex eight-year civil war, Israeli air strikes killed 15 people including civilians late Sunday, a monitor said.
The Syrian conflict has killed more than 370,000 people and drawn in world powers since it started in 2011 with the brutal repression of anti-government protests.
The United States has carried out several strikes in northwestern Syria, but they appeared to have petered out since 2017.
The US military said Monday it had targeted jihadists in an embattled opposition bastion in the northwest of the country the previous day.
"US forces conducted a strike against Al-Qaida in Syria (AQ-S) leadership at a training facility," US Central Command said in a statement.
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"This operation targeted AQ-S operatives responsible for plotting external attacks threatening US citizens, our partners, and innocent civilians," it added.
The Syrian Observatory for Human Rights said the raid in Aleppo province killed six commanders and other jihadists from the Hurras al-Deen group.
The leaders included two Tunisians, two Algerians, an Egyptian and a Syrian, the Britain-based monitor said.
Hurras al-Deen released a statement on social media channels on Monday saying a "group of brotherly jihadists" were killed in an attack on a "religious centre" and not a training facility.
Hurras al-Deen was established in February 2018 and has some 1,800 fighters, including non-Syrians, according to the Observatory.
It maintains ties to Al-Qaeda and fights alongside the global jihadist network's former Syria branch, Hayat Tahrir al-Sham.
HTS has since January controlled most of Idlib province as well as adjacent slivers of Aleppo, Latakia and Hama.
Late Sunday, Israeli air strikes near Damascus and in Homs province killed nine mostly foreign pro-regime fighters and six civilians, including three children, the Observatory said.
It was not immediately clear if the civilians died in the strikes or in their aftermath, it added.
The strikes hit several Iranian positions near Damascus, also targeting a research centre and a military airport west of the city of Homs where the Lebanese Shiite movement Hezbollah and Iranians are deployed, the war monitor said.
One of the pro-regime fighters killed was Syrian, while the rest were of other nationalities, Observatory chief Rami Abdel Rahman said.
State news agency SANA earlier said four civilians had been killed after its air defences responded to an Israeli attack.
An Israeli military spokeswoman declined to comment.
Israel has carried out hundreds of air strikes in Syria since the beginning of the conflict in 2011, targeting forces loyal to President Bashar al-Assad and the regime's allies Iran and Hezbollah.
On Monday, US Central Command pledged to continue targeting jihadists in Syria.
"Northwest Syria remains a safe haven where AQ-S leaders actively coordinate terrorist activities, to include planning attacks throughout the region and in the West," US Central Command said.
Syria analyst Sam Heller said the United States had effectively been excluded from the airspace over Idlib since President Donald Trump came to power.
Regime ally Russia "has prevented the US from launching the sort of targeted airstrikes it had carried out through the start of 2017," he said.
"It's not clear if this latest air strike signals that a new understanding has been reached, or if the US felt it especially urgent to bomb these militants in particular," Heller said.
The strikes come after both Trump and Russian President Vladimir Putin attended the G20 economic summit in Japan last week.
But Kremlin spokesperson Dmitry Peskov told AFP there was "no link" between the strike and Trump's meeting with Putin at the summit.
In March 2017, the Observatory said a US-led strike on a mosque in the north of Aleppo province killed 49 people, most of them civilians.
The Pentagon denied that it had targeted the religious building, acknowledging only one possible civilian death.
The US-led coalition has carried out tens of thousands of strikes against the Islamic State group in a campaign that saw the jihadists lose the last scrap of their cross-border "caliphate" in March.
The greater Idlib area was supposed to be protected by a buffer zone under a September agreement between Russia and Turkey.
But backed by Moscow, Damascus has since late April ramped up its bombardment of the region, home to some three million people.