Israel's Prime Minister Benjamin Netanyahu has ordered his military to "vigorously attack Hezbollah targets" in Lebanon, two days after a ceasefire was extended by three weeks.

Fresh Israeli attacks followed the directive, which came after at least six people were killed in strikes on southern Lebanon on Saturday.

Further cross-border exchanges between the two sides have strained the truce agreement, highlighting the precarity of the ceasefire.

The agreement, which has seen a reduction in fire rather than a complete halt, was extended on Thursday after talks between the countries' envoys in Washington.

Earlier on Saturday, Israeli strikes on a truck and a motorbike in the town of Yohmor al-Shaqeef in the Nabatieh district killed four people, Lebanon's health ministry said, according to Agence-France-Presse.

Another two people were killed and 17 injured in an attack on the town of Safad al-Battikh, in the Bint Jbeil district, it said.

The Israel Defense Forces (IDF) said it had "eliminated" three Hezbollah members on Saturday who were driving "a vehicle loaded with weapons", as well as another one riding a motorcycle.

It said two more armed members of the group were killed in the Litani area, where Israel has kept soldiers in the self-declared buffer zone, saying they "posed a threat to the IDF soldiers operating in southern Lebanon".

The IDF later said a "suspicious aerial target was identified" in the area of Malkia, adding the "incident constitutes an additional violation of the ceasefire".

Hezbollah, meanwhile, said it targeted an Israeli army vehicle in south Lebanon in retaliation for the attack on Yohmor al-Shaqeef, AFP reported.

Following Netanyahu's order to attack the group, Lebanon's state-run National News Agency (NNA) reported a pair of strikes in quick succession in a town in Bint Jbeil district, another on a town in Tyre district, and strikes on two more towns in Nabatieh district.

The Israeli military said it "struck Hezbollah terrorist infrastructure used for military purposes across southern Lebanon".

It said it would "continue to operate decisively against threats directed at Israeli civilians and IDF soldiers, in accordance with directives from the political echelon".

Israel continues to occupy a much of southern Lebanon and has been carrying out large-scale demolitions there.

An international press advocacy group said on Saturday attacks on journalists in Lebanon were "unacceptable", after a journalist was among those killed in Israeli attacks on Wednesday.

The Media Freedom Coalition (MFC), a partnership of countries including the UK, urged all parties to allow members of the media to work freely and safely.

A statement from the co-chairs said: "The UK and Finland strongly condemn all violence directed against journalists and media workers."

An Israeli strike killed Amal Khalil, who worked for a Lebanese newspaper, and injured freelance photographer Zeinab Faraj.

Officials in Lebanon say they were deliberately targeted as they sought shelter in a home after an initial air strike hit the vehicle in front of them, killing two men.

The IDF said it did not target journalists.