CAIRO: A bomb blast just beside Egypt’s foreign ministry killed three policemen on Sunday, authorities said, in the most serious attack in Cairo in almost three months.

There was no immediate claim of responsibility for the bombing, which killed two police lieutenant colonels and a recruit, according to the foreign ministry. But the operation resembled ones carried out by insurgents seeking to topple the U.S.-backed government, underlining security challenges facing President Abdel Fattah al-Sisi, who has just completed 100 days in office.

Sisi has pushed through some badly-needed economic reforms such as a rise in fuel prices. But tackling militants - an issue that has dogged one Egyptian leader after another - is far from easy.

Egypt has faced rising militant violence since Sisi deposed President Mursi last year after mass protests against his rule and cracked down on his Muslim Brotherhood movement.

The challenge has become more complex since Islamic State militants seized parts of Iraq and Syria in June and declared a caliphate, inspiring other militant groups including some based along Egypt’s border with chaotic Libya. Islamic State established ties with Sinai-based Ansar Bayt al-Maqdis and has been coaching Egypt’s most lethal militant organisation, security officials and an Ansar commander told Reuters.

Smoke rose and people ran after Sunday’s blast along a sidewalk in the neighbourhood of Boulaq bu Eila, just behind the Foreign Ministry, which is located in a high rise building beside the Nile. There was no damage to the Foreign Ministry building and work was proceeding normally, though security had been tightened, a source in the ministry told Reuters. Airport authorities said they were also taking greater precautions.

The last significant attack in Cairo was on June 30, when two policemen died trying to defuse bombs planted by militants near the presidential palace. Sunday’s blast caused a tree to fall on a car. Blood stained a busy intersection beside a crowded market. While the death toll was low, any attack in the capital is bound to cast doubt over the effectiveness of security forces, who have vowed to end militant bloodshed that has hammered the tourism industry, a pillar of the economy.

Sisi has repeatedly expressed concerns about militancy in Egypt and other parts of the Middle East. Security forces have killed hundreds of Muslim Brotherhood supporters, arrested thousands and put top leaders on trial, severely weakening what was once Egypt’s most organised political group. But tackling Ansar and other militant groups has proven more difficult despite several army operations. The Brotherhood says it is committed to peaceful activism.

Egyptian authorities make no distinction between the Brotherhood and groups such as Ansar, which has in recent weeks beheaded several people it has identified as spies for Israeli intelligence, suggesting it has become more radical. The Egyptian state has crushed militant groups in the past but they often recover.

In the 1990’s, militants staged attacks against government officials and foreign tourists. It took then President Hosni Mubarak years to defeat them. Egypt suffered other losses on Sunday. Six soldiers were killed after a military aircraft crashed due to a technical failure, the army spokesman said. Moreover, an Egyptian military aircraft crashed on a training mission on Sunday after a technical failure, killing six soldiers, the army said. The aircraft came down about 100 kilometres (60 miles) south of Cairo, an army statement said.

‘During military training, a technical failure led to the crash of an aircraft carrying troops in Kom Aushim in Fayoum province killing six soldiers and injuring one,’ the army said. No further details about the accident, including the type of the aircraft, were immediately available.

Army Chief Sedky Sobhy ordered an investigation into the crash, the statement added. On January 25, five soldiers were killed when their helicopter was shot down by militants in the Sinai Peninsula where troops are battling an insurgency.

Militants have carried out deadly attacks against security forces in the peninsula and in cities including Cairo since the army ousted president Morsi in July last year. On Sunday, two policemen were killed and six people were wounded when a bomb exploded near a checkpoint outside the foreign ministry headquarters in the capital.