A massive suicide truck bombing rocked a highly secured diplomatic area of Kabul, killing 90 people and wounding as many as 400. The attack left a scene of mayhem and destruction in the Afghan capital.

A look at some of the lingering issues after Wednesday’s attack:

Looking for answers

Investigators will seek to understand how insurgents managed to get an explosives-packed tanker truck into one of the best-protected areas of Kabul. The Wazir Akbar Khan district is home to most of the capital’s foreign embassies as well as several major government institutions, including the Presidential Palace.

“No one could even imagine that would take place in Wazir Akbar Khan,” said Gen. Mirza Mohammad Yarmand, a former deputy interior minister. “I would call it a security and intelligence error.”

Questions about ability to protect the capital

The bombing raises serious questions about the Afghan government’s ability to provide basic security. Insurgent groups have been on the offensive ever since the drawdown of NATO troops from the country in 2014.

The first half of 2017 has seen a particularly successful string of extremist attacks in the capital, including a twin suicide bombing March 1 that killed 22 people and a coordinated March 8 assault on a military hospital that killed 50 people.

No claim of responsibility

As of late Wednesday night in Kabul, no one had claimed responsibility. The vast majority of such devastating attacks recently have been undertaken by either the Taliban or the local affiliate of Islamic State group.

The Taliban has been waging a guerrilla war against Kabul for more than a decade ever since being ousted from power by a U.S. invasion in 2001 in the aftermath of 9/11. The Islamic State group is a more recent development, forming in the last few years and largely made up of dissident former Taliban militants. IS has been battling the Taliban for control of certain parts of Afghanistan while also regularly targeting the government.

Also Read Blast hits Kabul’s diplomatic quarter

Yarmand said he didn’t believe the Taliban were behind it, saying they “don’t have the ability to carry out such big attack, and if they did, they would have claimed responsibility.”

The former Interior Ministry official repeated a common belief among Afghan government officials that the Pakistani intelligence services have played a role in the string of extremist attacks plaguing Kabul. Pakistani officials have repeatedly denied such accusations.

Attempts at diplomacy

So far, it doesn’t appear likely.

There have been multiple attempts to launch peace talks between the Afghan government and the Taliban, but all have faltered. The most recent initiative, brokered by Pakistan, collapsed and spawned even more public distrust and animosity between Kabul and Islamabad.

What’s more, as long as the Taliban and other insurgent groups can demonstrate the ability to strike deep in the heart of the most secure parts of Kabul, the impetus to negotiate will likely be reduced. Yarmand said there doesn’t appear to be much desire to negotiate on the part of the Taliban leadership or its rank and file.

“For now, their supporters need them to be in the fight with the Afghan government,” he said.