Increased violence in and around the Gaza Strip, where an overnight air strike killed a Palestinian militant, have prompted blunt warnings from Israel as fears grow of another major confrontation.
The latest Israeli raid -- one of nearly a dozen this month -- comes after cross-border exchanges killed several Palestinians and one Israeli little more than a year after a November 2012 conflict forced Gaza's Islamist rulers Hamas into a fragile ceasefire.
Israel warned it will use "any means" to stop rocket fire from the besieged Palestinian territory, with Prime Minister Benjamin Netanyahu holding Hamas entirely responsible for such attacks, and threatening to teach it a lesson "very soon".
Medics said an Israeli air strike killed two Palestinians including one militant in northern Gaza early Wednesday.
Ahmad al-Zaanin, 21, and Mahmud al-Zaanin, 23, died when a missile struck their car as they were driving around the northern town of Beit Hanun, a spokesman for the Hamas-run health ministry said.
Israel's military said the attack targeted Ahmad al-Zaanin and described him as "a senior operative in the PFLP terror organisation" responsible for recent anti-Israeli attacks and who posed an "imminent threat" to civilian lives.
It said Zaanin was behind rocket fire on January 15 which struck open ground shortly after the funeral of former premier Ariel Sharon, which took place several kilometres (miles) from the Gaza border.
A separate Palestinian militant group, Islamic Jihad, claimed Ahmad al-Zaanin as a member, confirming his death and that of "one of his relatives Mahmud al-Zaanin" in the strike "near his home".
The PFLP did not immediately claim Zaanin as a member.
Israel has continued to target Islamic Jihad, Hamas weapons stockpiles and training camps since a ceasefire with Gaza's ruling movement took effect after a bloody eight-day conflict in November 2012.
Netanyahu vowed to teach Hamas a lesson "very soon" if attacks continue, saying that Israel's policy of retaliating "forcefully" against rocket fire from Gaza had produced "a quiet year in 2013".
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"If Hamas and the terror organisations have forgotten this lesson, they will learn it again powerfully very soon," he said on Tuesday.
Defence Minister Moshe Yaalon echoed Netanyahu's remarks, saying Israel would use "any means" against Gaza.
"We will not hesitate to use force to combat those who threaten our security, and we will do this using any means we possess," he said in a statement, calling Wednesday's strike "another stage in our fight against rocket fire".
Yaalon's deputy Danny Danon said: "Those who engage in terrorism will pay a high price for their actions."
Israel has insisted that Hamas will be held entirely responsible for any rockets fired from the enclave.
On Tuesday, Hamas said it had deployed forces to "preserve the truce."
But experts said the Islamist movement might have trouble restraining rocket fire from Gaza, given the pressure it is under not to kowtow to its sworn enemy.
"Israel's decision to go back to a policy of targeted assassinations, targeting Palestinians who are suspected of launching rockets... will gradually lead to a dangerous escalation between the Gaza Strip and Israel," said Mkhaimer Abu Saada, a political science professor at Gaza's Al-Azhar University.
"There will be retaliation from other groups, but Hamas will even find it difficult to control its own (armed wing the) Ezzedine al-Qassam Brigades."
Over the past month, tensions have soared in and around Gaza after more than a year of relative calm.
Since December 20, six Palestinians and an Israeli have been killed in violence in and around the territory, with militant rocket fire sparking retaliatory air strikes.