At least three Palestinian police officers were killed and three others were wounded as two explosions hit police checkpoints near Gaza City late Tuesday night, according to authorities in the Hamas-run enclave.

The Israel Defense Forces denied involvement in the blasts, saying it was “unaware of any strikes” in Gaza.

Gaza’s Hamas-run interior ministry said the first explosion occurred next to a police checkpoint south of Gaza City.

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“Two members of the police were martyred as a result of an explosion that took place near a police checkpoint at the Dahdouh intersection,” Hamas-run Interior Ministry spokesman Iyad al-Bozm said.

The Strip’s Hamas-run Health Ministry said two people were killed and a third man suffered serious injuries in the explosion. The ministry initially blamed the blast on Israel, but later retracted the claim.

Minutes later another blast hit a second police checkpoint west of Gaza City, wounding three people, the Interior Ministry spokesman said.

One of those injured later succumbed to his wounds.

“The security forces, including the police, are carrying out investigations at both places where explosions occurred,” the spokesman said.

The dead in both explosions were identified as Salameh al-Nadim, 32, Wael Khalifa, 45, and Alaa al-Gharbali, 32, all traffic policemen.

Following the blasts Hamas put all its forces on alert.

“Mobilization of all police and security forces has been declared to follow-up on security developments in the aftermath of the two explosions,” said al-Bozm.

Hamas leader Ismail Haniyeh called on people to be patient while the investigation was ongoing and not to spread rumors.

“In a short amount of time, the situation will be clear to our people, who we urge, as we have regularly done, to maintain its cool, especially as we are supported by strong security forces that are able to handle the circumstances and deal with it in a forceful and wise manner,” he said.

“We need to support our security forces in restoring security and order and foiling this damned plot,” he said.

Tawfiq Abu Naim, the head of the Hamas-run security forces in Gaza, is currently in Cairo for talks with Egypt.

It was not immediately clear who was behind the attacks, but the Hamas-rulers of the impoverished Strip frequently crack down on dissent due to the dire economic situation. There are also frequent tensions with extremist Salafist groups who want greater conflict with Israel.

An interior ministry statement later called the bombings isolated incidents and said that they had initial information on the identity of the attackers, but did not release further details.

“We reassure our people the security situation is stable in the Gaza Strip and affirm that these suspicious explosions–that seek to cause confusion in the internal arena–are isolated events that will not impact this [stable security] situation,” the statement said. “The wicked hands that perpetrated this crime will not evade punishment”

The explosions also come amid heightened tensions between Israel and terror groups in the Strip, following a series of rocket launches and attempted cross-border attacks by Palestinian gunmen.

On Tuesday, four mortar shells were fired at Israel, one of which landed in the south. The army responded by targeting a Hamas site.

On Sunday night, three rockets were fired from Gaza into southern Israel, causing some damage but no injuries, and sending hundreds of concert-goers in the southern city of Sderot running for cover. Those rockets prompted reprisal Israeli strikes, and on Monday, Israel’s military liaison to the Palestinians announced it had reduced fuel shipments to the Gaza Strip’s sole power plant.