CAIRO (AFP) - Mexican President Enrique Pena Nieto expressed his nation's "outrage" at the killing of eight tourists by Egyptian security forces as his foreign minister arrived in Cairo on Wednesday (Sept 16) demanding an urgent inquiry into the "unjustified attack".

Egyptian authorities said security forces chasing militants mistakenly killed a total of 12 Mexicans and Egyptians whose convoy had entered a restricted area of the vast Western Desert on Sunday.

Survivors told Mexican diplomats they were bombed by a plane and helicopters.

Egyptian President Abdel Fattah al-Sisi called Pena Nieto to express his "most sincere condolences" over the "tragic incident," the Mexican leader's office said in a statement.

"President Pena Nieto expressed his deep dismay and sadness over the death of our citizens, as well as the pain and outrage that these unprecedented events have caused within Mexican society," the statement said.

The Mexican leader reiterated his call for an exhaustive and swift investigation into what happened.

His Foreign Minister Claudia Ruiz Massieu landed early Wednesday in Cairo for talks with top Egyptian officials to "clear up the circumstances of this deplorable event, which has cost the lives of innocent Mexican tourists".

Ruiz Massieu, who was accompanied by relatives of four of the victims, would visit the six Mexicans wounded in the attack at their hospital in a suburb of Cairo, a senior official travelling with her told AFP.

Egypt said the tourists entered a restricted area in the Western Desert and were "mistakenly" killed as security forces chased militants who had abducted and beheaded an Egyptian.

The incident has proven embarrassing for security forces which regularly claim to have killed dozens of militants in air strikes, tolls that are difficult to independently verify.

POLICE ESCORT

Hassan al-Nahla, head of Egypt's tour guides union, said the tourist group had received all the required permits and set off with a police escort from Cairo to Bahariya oasis, roughly 350 km away.

About 80 km from their hotel, they veered 2 km into the desert for lunch, he said in a statement.

The place they chose for their picnic was a regular tourist stop, Nahla said later on television.

"I don't blame anyone but I ask who is responsible for coordination, and why was it absent?

"If the military is dealing with terrorists, why were the authorities who issue permits not notified? Why was the tourism ministry not notified so it could coordinate with the tourism companies?" Nahla told AFP the area where they stopped had never been a restricted zone.

"There was no notification on the ground, and no coordination," he said of the security operation.

The incident is likely to raise further fears for Egypt's vital tourism industry, which has struggled to recover from years of turmoil.

About 10 million tourists visited Egypt in 2014, down sharply from almost 15 million in 2010.

Many Egyptians on social media have criticised the government for suggesting the tourists were at fault for straying into a restricted zone.

The Western Desert is popular with tour groups, but is also a militant hideout, with Western embassies warning against non-essential travel there.

Last month, Egypt's branch of the Islamic State in Iraq and Syria beheaded a Croatian oil worker who was abducted near Cairo, at the edge of the Western Desert.

ISIS in Egypt said on Sunday it had "resisted a military operation in the Western Desert" and published pictures of its fighters apparently engaging the military.

Egypt has struggled to quell a militant insurgency focused mainly in the Sinai Peninsula in the east since the military overthrew Islamist president Mohamed Morsi in 2013.

The military last week launched a wide-scale campaign to uproot militants in the peninsula, claiming to have already killed more than 200 jihadists.

Nine soldiers, including one killed in a roadside bombing on Monday, have died in the operation, it said.

Cairo says hundreds of police and soldiers have been killed, many in attacks claimed by ISIS's Sinai Province affiliate which pledged allegiance to the main group in Iraq and Syria last year.