Police in Gaza are investigating a deadly explosion which came hours after a ceasefire was reached between Israel and armed groups in the territory.
Hamas and Islamist militants announced the agreement late on Saturday after Egyptian and international efforts to secure a truce, but it did not take long for doubts to emerge over whether it would hold.
Warning sirens were heard in southern Israel in the early hours of Sunday, indicating more rocket fire, before the blast at a house west of Gaza City.
It resulted in the deaths of a 35-year-old man and his son, 13, but the cause is unclear and officers have not suggested whether Israel was responsible.
The country carried out dozens of airstrikes against the Palestinian enclave's ruling Hamas group on Saturday and gunmen fired more than 100 rockets across the border, with two teenagers reported dead.
Israeli Prime Minister Benjamin Netanyahu - who has not commented on the ceasefire - said they were "the hardest strikes" against Gaza since 2014.
They left smoke billowing above the Gaza Strip, with Israeli Defence Forces (IDF) confirming that they had launched strikes against multiple militant sites in response to renewed violence along the border.
It said its jets targeted a Hamas tunnel in the southern portion of the Strip early on Saturday morning, alongside Hamas military compounds.
The violent exchanges left 12 people injured, in addition to the two dead teenagers, with three Israelis wounded by a rocket which landed in Sderot.
Mr Netanyahu said: "The IDF has struck Hamas with the hardest blow since Operation Protective Edge and we will increase the strength of our attacks as necessary".
Hamas said it fired rockets to discourage Israel from taking further action.
Such rocket attacks have become a regular feature of the asymmetric conflict between Hamas and Israel, driving the IDF to develop the Iron Dome defence system to intercept and destroy incoming rockets.
According to the IDF, a military officer was lightly wounded by a grenade thrown at the border on Friday.
On the same day, a 15-year-old Palestinian boy was shot dead as he reportedly attempted to climb the fence into Israel.
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