A clash seems to be looming between Israel and the radical Palestinian movement Islamic Jihad, as they abandon pledges made under a fragile ceasefire that ended the last full-scale war in the Hamas-run Gaza Strip.
Israel recently targeted two of the group's militants for firing rockets at it, and Prime Minister Benjamin Netanyahu promised to teach Gaza-based militants a "lesson."
Islamic Jihad has in turn threatened to take its war to Israel and the Israeli-occupied West Bank.
It said it plans to carry out suicide attacks in Israel, for which it was notable during the Palestinian intifada that killed Israelis and thousands of Palestinians at the beginning of the last decade.
And it has threatened to incite unrest in the Israeli-occupied West Bank, whose governing Palestinian Authority is in faltering peace talks with Israel.
In the latest violence, Islamic Jihad said Israel killed one of its militants, Ahmad al-Zaanin, and his cousin in an air strike in the northern Gaza Strip Wednesday.
Israel said Zaanin was behind rocket attacks on the Jewish state and an "immediate" danger to Israeli civilians.
In response, Islamic Jihad said the "blood of our martyrs will not have been shed in vain."
At the time, Netanyahu promised Gaza groups, including the besieged enclave's rulers Hamas, that they would learn a lesson "very soon" if rockets continued to be fired, referring to Israel's policy of retaliating "forcefully."
The security correspondent for Israel's Yediot Aharonot daily said the strikes marked an escalation on Israel's part.
"Ever since Operation Pillar of Defence (in 2012), there was an understanding with Hamas that no targeted killings would take place as long as the quiet was maintained," he wrote.
"The moment it became clear that Hamas was losing control of the Gaza Strip -- this weapon was again pulled out."
"Targeted killings are the most effective means of dissuasion against the organisers of terrorism, especially in the Gaza Strip where the Israeli army cannot go in and make arrests," as in the West Bank.
Islamic Jihad spoke in similarly shrill tones, promising suicide attacks in Israel.
"The decision to carry out suicide operations in Zionist cities is one that is irreversible," said Abu Ahmad, a senior commander in the group's Al-Quds Brigades.
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"The operations will put pressure on the Palestinian leadership, but will also deter the enemy, and we're continuing to try to carry them out," he told AFP.
"We have a high level of weaponry with which to strike deep in the Zionist entity and send messages threatening it."
On December 22, a bomb exploded on an empty bus in the Israeli coastal city of Tel Aviv.
No Gaza group claimed responsibility, but Israel's Shin Bet internal security service arrested four men in the West Bank town of Bethlehem, saying they were an Islamic Jihad cell behind the attack.
Meanwhile, Islamic Jihad spokesman Dawud Shihab told AFP the group would incite West Bank Palestinians to rise up against their occupiers.
It "will rouse the masses and prepare them for the next confrontation with the occupation, and for the outbreak of a new intifada.
"There will be an explosion in the face of the occupation in the West Bank, because of the failure of the PA and Israel's monstrousness," he said.
But various Palestinian factions are still divided and mired in internal squabbles.
The PA, based in the West Bank, is in deadlocked US-backed peace talks with Israel, which Hamas firmly opposes.
Gaza groups accuse the PA of colluding with Israel in the arrest of West Bank-based militants, although it publicly bemoans Israel's lack of consultation with it on joint security efforts and insists it does not unjustly target Palestinians.
Even within Gaza, relations are complex. Islamic Jihad -- inspired by Iran's 1979 revolution and formed the following year -- sometimes cooperates and is sometimes at odds with the Muslim Brotherhood-allied Hamas, formed in the late 1980s.
The death of an Al-Quds Brigades commander from wounds sustained during a police raid on his house in June caused a temporary spat between the groups, before they publicly patched up their differences.
Islamic Jihad claims to have 8,000 fighters in its military wing, making it the second largest armed group in Gaza behind Hamas.
Unlike smaller Salafist factions, Islamic Jihad has so far respected an Egypt-brokered truce between Hamas and Israel that ended the 2012 conflict.