France on Tuesday increased its estimate of the number of its nationals embroiled in Syria's civil war to more than 800 and warned that they pose an unprecedented security threat.

The warning, from Prime Minister Manuel Valls, followed the weekend arrest of Medhi Nemmouche, a French jihadist suspected of carrying out last week's Brussels Jewish Museum killings after spending a year fighting in Syria.

Several Israeli ministers on Tuesday lashed out at Washington over its decision to work with the new Palestinian unity government which is backed by the Islamist movement Hamas.

"Unfortunately, American naiveté has broken all records. Any collaboration with Hamas which kills women and children is unacceptable," said Communications Minister Gilad Erdan, a security cabinet member considered close to Prime Minister Benjamin Netanyahu. 

Israeli security forces killed a Palestinian man after he shot and wounded a border guard in the northern West Bank late Monday, the army said.

"An armed Palestinian opened fire at the Tapuach junction and wounded an Israeli border guard," said an army spokeswoman. "Soldiers and border guards returned fire and killed the assailant."

Lebanese Forces leader Samir Geagea on Monday condemned what he described as the "insolent campaigns" that are targeting Maronite Patriarch Beshara al-Rahi over his controversial visit to the Holy Land and Israel, saying he will maintain contacts with Bkirki in a bid to put an end to the ongoing presidential vacuum.

According to a statement issued by his press office, Geagea telephoned al-Rahi, expressing his “strong condemnation of the campaigns that are targeting His Eminence” and describing them as “insolent campaigns that breach all Lebanese norms and traditions.”

Progressive Socialist Party leader MP Walid Jumblat defended on Monday Maronite Patriarch Beshara al-Rahi's recent trip to the Holy Land, questioning the uproar created over the visit and the failure of the majority of the parties to defend him.

He said in his weekly editorial to the PSP-affiliated al-Anbaa website: “Al-Rahi's trip was inevitable given the negative repercussions the security and political developments in Palestine, Syria, and Iraq are having on the region's Christian population.”

Rocket fire from Gaza and Syria hit Israel early Monday in two separate incidents that prompted the Israeli military to hit back, just hours before the swearing in of a new Palestinian government.

The exchanges of fire took place as Palestinian president Mahmoud Abbas was to unveil a new government pieced together as part of a surprise April reconciliation agreement between leaders in the West Bank and the Hamas-run Gaza Strip, that has been fiercely opposed by Israel.

A long-awaited Palestinian unity government was sworn in before President Mahmoud Abbas on Monday after a landmark reconciliation deal with the Islamist Hamas that has infuriated Israel.

Following a ceremony at the Muqataa presidential compound in Ramallah, Abbas hailed "the end" of a bitter and sometimes bloody divide between his Fatah movement and the rival Hamas which rules Gaza.

Head of Hizbullah's Juristic Committee Sheikh Mohammed Yazbek on Sunday stressed that only the Lebanese state can condemn or acquit the Lebanese who fled to Israel in 2000, responding to recent remarks by Maronite Patriarch Beshara al-Rahi.

“The Israeli enemy used these Lebanese to kill other Lebanese … and when the liberation happened, we said back then that this issue is in the hands of the state,” Yazbek said during a memorial service in Baalbek.

Palestinian and Israeli rights groups on Sunday wrote to EU foreign policy chief Catherine Ashton demanding her "urgent intervention" on behalf of 125 prisoners on long-term hunger strike.

The letter was sent as the overall number of Palestinian prisoners refusing food climbed to 290, including 70 being treated in hospital, an Israel Prisons Service spokeswoman told Agence France Presse.

World governments should not rush to approve the new Palestinian government, Israeli Prime Minister Benjamin Netanyahu warned Sunday after the Palestinians accused Israel of looking to punish them over a unity deal. 

"I call on all responsible elements within the international community not to hurry to recognize the Palestinian government that Hamas is part of, and which relies on Hamas," Netanyahu told ministers at the weekly cabinet meeting, saying it would "strengthen terror".