An explosion in Gaza killed six people on Saturday, Hamas said. It blamed the incident on Israel, which declined comment.
A statement from the Palestinian group's armed wing called the incident a "deplorable Zionist crime" perpetrated against its people.
"During a complicated security and intelligence operation conducted by Qassam Brigades to investigate a serious and a grave security incident conducted by the Zionist enemy against Palestinian resistance, a deplorable crime took place against our Mujahideen in the area of Zawayda in central Gaza Strip," it said.
Reuters television captured a pillar of smoke rising above the village of Zawayda near the coast of Gaza, far from the border with Israel where tensions have escalated in recent weeks.
The exact circumstances of the blast were unclear and Hamas, which controls the Gaza Strip, provided no further details.
An Israeli military spokesman declined to comment on the incident, although a more junior official had earlier denied the army was involved.
Israel withdrew its troops and settlers from Gaza in 2005. But, 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.
In co-ordination with Israel, Egypt also keeps its border with Gaza largely closed.
Forty-three Palestinians have been shot and killed by Israeli forces since March 30, when Gazans began weekly protests dubbed "The Great March of Return" along the border with Israel.
Facing international censure over its use of live fire in the protests, Israel says it is protecting its border and takes such action only when protesters, some hurling fire-bombs and trying to plant explosives, come too close.
As Israel celebrates its 70th birthday, Palestinians mourn what they call the "Nakba" (Catastrophe) of their people's mass dispossession during the conflict that broke out in 1948.
Two-thirds of the 2 million Palestinians in Gaza are war refugees or their descendants. The protests have seen thousands gather to demand access to their families' lost homes or lands, now in Israel.
Israel says Hamas is using the protests as cover to try to carry out attacks. Hamas denies the accusation.