The UN's special coordinator for the Middle East peace process said on Wednesday that ongoing escalations undermined efforts to improve socio-economic conditions in Gaza.
"I am very concerned about the ongoing and serious escalation between Palestinian Islamic Jihad and Israel, following the targeted killing of one of the group’s leaders inside Gaza yesterday," Nickolay Mladenov said in a statement.
Mladenov stressed that there could be no justification for any attacks against civilians.
"The indiscriminate launching of rockets and mortars against population centers is absolutely unacceptable and must stop immediately.
"The continuing escalation is very dangerous. It is yet another attempt to undermine the efforts to improve the dire socio-economic conditions in Gaza and prevent another devastating conflict," he added.
He also said the UN was trying to urgently de-escalate the situation.
At least 26 Palestinians have been martyred and 85 others -- including 30 children and 13 women -- injured in Israeli raids on the blockaded strip since Tuesday.
The situation escalated in Gaza early on Tuesday after an Israeli airstrike killed Bahaa Abu al-Atta, the commander of resistance group Islamic Jihad, as well as his wife Asmaa Abu al-Atta.
Israeli warplanes also launched an airstrike targeting Islamic Jihad member Akram al-Ajouri in Syria’s capital Damascus.
Two people, including al-Ajouri's son, were killed and 10 injured, but the Islamic Jihad leader emerged unhurt.