The Palestinian Islamic Jihad militant group says four of its members were killed in an apparent accidental blast in the Gaza Strip.
The group said in a statement on Saturday that it was "mourning its fighters who were martyred during preparations".
It usually employs those terms to refer to casualties caused by the accidental detonation of weapons or explosives used in attacks against Israel.
The Gaza health ministry confirmed four fatalities in the incident. Medics at the scene in the Rafah area said the explosion was caused by Israel. But an Israeli military spokesman said the army was not involved.
"Contrary to reports currently circulating I can tell you that the IDF (Israel Defence Forces) is not aware of any IDF fire in the area surrounding Rafah," the spokesman said.
Violence has flared in the Gaza Strip since March 30, when Palestinians began protests along the border area with Israel.
Israeli troops have shot dead 31 Gaza Palestinians and wounded hundreds since the protests began, drawing international criticism of their lethal tactics.
The border area remained largely quiet on Saturday.
Protesters have set up tented camps near the frontier as a protest dubbed "The Great March of Return" - evoking a longtime call for refugees to regain ancestral homes in what is now Israel - moved into its third week.
Israel has declared a no-go zone close to the Gaza border fence.
Israel withdrew its troops and settlers from Gaza in 2005. The Palestinian enclave is ruled by the Islamist Hamas movement, designated by Israel and the West as a terrorist group.
Citing security concerns, Israel maintains a naval blockade of the coastal territory, keeping tight restrictions on the movement of Palestinians and goods across the frontier.
Egypt, battling an Islamist insurgency in neighbouring Sinai, keeps its border with Gaza largely closed.
