Gunmen have seized four members of the Palestinian Islamic group Hamas from a bus bound for Cairo from the Gaza Strip, an Egyptian security official said on Thursday.

The identity of gunmen, who stopped the bus close to the Rafah border crossing with Gaza on Wednesday night, was not immediately clear.

Hamas blamed Egypt for the abductions which it described as a “security coup” that could further strain relations with Cairo.

The Egyptian security official said the four men shot at the bus, forcing it to a halt, before assaulting the driver and kidnapping the Hamas members after checking their identity documents.

The bus was carrying 50 passengers.

Officials said the kidnappers were wearing “Pakistani-type” clothes. Some militants in Sinai dress in tunic-style fatigues that are common in Pakistan and Afghanistan.

It was unclear whether the bus had a police escort when the gunmen intercepted it, as Hamas claimed in its statement.

The road from the Rafah border crossing, which Egypt occasionally opens, runs through the lawless North Sinai where Islamic State group jihadists are waging an insurgency.

The incident rattled Gazans who rarely have a chance to leave the coastal strip.

“This event is worrying, because I’m with my children... I’ll wait until it’s safe to travel,” said Rasha al-Qedra, a woman on the Palestinian side of the crossing.

The Islamic State of Iraq and Syria (ISIS) group has threatened Hamas after it arrested jihadist militants suspected of targeting its armed wing with a series of bombings.

But Hamas’s statement lay the blame on Egypt, saying it had been in touch with Cairo to ensure the return of the abducted men.

“They had entered the crossing after receiving permission from Egyptian security forces, which could have prevented them from entering,” said Hamas.

Relations between Hamas and Egypt have deteriorated since the military overthrew Islamist president Mohamed Morsi in 2013.

Morsi, a leader of the Muslim Brotherhood, had been sympathetic to Hamas, the Palestinian offshoot of his movement.

His overthrow unleashed a deadly crackdown on Islamist protesters, and an insurgency based in Sinai.