At least 42 people have been killed in air strikes in north-west Syria, reports say.
Syria's defence ministry said Israeli planes targeted several sites in the Aleppo countryside at 01:45 on Friday (22:45 GMT Thursday).
A UK-based monitoring group said Hezbollah militants and Syrian soldiers died as a Hezbollah arms store was hit.
Hours later, Israel's military said it had killed a senior Hezbollah figure in an air strike in Lebanon.
Ali Abed Akhsan Naim was a deputy commander of the group's missiles and rockets unit, the Israel Defense Forces said, and was responsible for conducting and planning attacks on Israeli civilians.
Video released online by Israel showed a moving vehicle, which he was said to be travelling in, exploding after being struck by a missile.
The strike was in the Bazuriyeh area, east of the port of Tyre, the IDF added.
Hezbollah has not yet commented on the reports.
The Syrian Observatory for Human Rights (SOHR) - which monitors events in Syria from the UK - said the Aleppo attack had led to the highest number of dead (36) among Syrian forces in a single such "Israeli attack". It also said six Hezbollah fighters were killed.
Citing two security sources, Reuters news agency said five Hezbollah fighters were among the dead, putting the death toll at 38.
Syria's defence ministry said civilians and Syrian military personnel had been killed. It said the air strikes were carried out "in conjunction with" drone attacks by "terrorist organisations" against Aleppo city and the surrounding area, though it did not give any further information.
Israel's military told the BBC it would not comment on foreign media reports.
The SOHR, which uses an extensive network of contacts in Syria, said the alleged Israeli strikes also caused multiple injuries, some serious.
It said that the strikes hit the weapons warehouse in Jabrin area, near Aleppo international airport, and targeted Syrian air defence forces facilities in Al-Saferah, about 20km (12.5 miles), south-east of Aleppo city. It also said explosions were heard in the Kafr Joum area of western Aleppo.
In recent years, Israel has launched hundreds of strikes on Syria against Hezbollah or Iranian assets there. It has vowed to prevent Iran - Hezbollah's most important backer - from transferring advanced weaponry to the Lebanese group or from building up its own military presence in Syria.
Both Iran and Hezbollah - Syrian allies - oppose Israel's existence. Alleged Israeli strikes on Syria have increased since Hamas, which is also supported by Iran and Hezbollah, carried out the 7 October attacks on Israel, which triggered the war in Gaza.
Cross-border attacks between Hezbollah in Lebanon and Israel have also escalated. On Wednesday, Israeli air strikes on southern Lebanon killed 16 people, including Hezbollah fighters and other militants, marking the deadliest attacks of their kind since Hezbollah began launching rockets at Israel in support of Hamas on 8 October.
Hours after the first Israeli strike, a Hezbollah rocket barrage killed a 25-year-old man in northern Israel.