Three rockets fired from the Gaza Strip have hit southern Israel, hours after Israeli forces killed two Palestinians in the West Bank.
Tuesday's incidents cast doubt over the future of a fragile truce that has been in force in Gaza between Israel and armed Palestinian groups during the last five days.
Al-Quds, the military wing of the Islamic Jihad movement, took responsibility for the rocket attacks which caused some damage but no casualties in the Israeli town of Sderot.
David Baker, a spokesperson in the Israeli prime minister's office, said: "Any rocket fire from the Gaza Strip would be a grave violation of the calm."
The rocket attacks followed an Israeli raid into the West Bank town of Nablus earlier during the day.
Israeli troops killed the men in an exchange of fire, an Israeli military spokesman said, adding that one of them was a fighter from Islamic Jihad and the other was a "militant".
Hamas, the main signatory of the Gaza truce, condemned the Israeli killings.
However, they called on Palestinian factions "to exercise self-restraint and continue observing the agreement".
Nablus residents said that one of the men was a bystander killed by Israeli troops when he opened the door to his apartment, which lies next to the location of the raid.
The truce between Israel and Palestinian armed groups, including Hamas, does not cover the West Bank.
|Tareq Abu Ghali was one of the Palestinians killed in Nablus [AFP]
The Islamic Jihad movement had said that the killings would not pass without punishment.
In a statement, the group said that the truce does not mean Palestinians would sit silently.
It called on different Palestinian factions to clarify their position regarding the latest Israeli attack.
Ayman Mohyeldin, Al Jazeera's correspondent in the Gaza Strip, said there was no confirmation from either side that the violence had rendered the ceasefire void.
Lamis Andoni, Al Jazeera's Middle East analyst, said: "The killings are a reminder that the truce in Gaza will remain shaky when it is not extended to include the West Bank.
"Israeli insistence on retaining freedom to conduct arrests and raids in the West Bank further undermines Palestinian president Mahmoud Abbas' standing, and makes it difficult for Hamas to demand Palestinian fighters adhere to the truce in Gaza."
A mortar shell was also fired into Israeli territory from the Gaza Strip the previous evening, the Israeli army said, in the first such incident since the truce came into effect on June 19.
No one was hurt by the missile, which landed in the Nahal Oz area after being launched from the central Gaza Strip, officials said on Tuesday.
"We are familiar with a mortar shell that landed near the security fence in northern Gaza on the Israeli side," an army spokeswoman said.
There has been no claim of responsibility for the reported incident on Monday evening, nor any confimation from Palestinian sources that such an incident took place.
Observers have said that both sides do not regard the incident as a violation of the ceasefire.