Kabul, Afghanistan (CNN) A day after a massive suicide blast that left at least 90 dead , angry residents of Kabul were counting the cost of another brutal attack on their city -- and asking how it was allowed to happen.

The bombing, which struck Kabul's diplomatic quarter during rush hour on Wednesday morning, came just a few days into Ramadan, a time when Muslim families come together to observe the holy month.

Instead, relatives were burying the dead and tending the wounds of the 461 confirmed injured.

Injured Afghan men receive treatment at a hospital in Kabul on Thursday, a day after the truck bombing.

Most of the wounded were taken to the city's three major hospitals, where emergency wards remain packed with those caught up in the massive blast. As doctors worked around the clock, hospitals sent out urgent calls for more blood to treat many with critical injuries.

No group has yet claimed responsibility for the attack, which saw a waste water truck crammed with explosives detonated in one of the busiest streets in the city.

By Thursday morning, Afghan security forces had cordoned off streets hundreds of meters from the site, and workers were busy filling in the crater left by the blast, as large trucks loaded with barrels of tar drove into the area. Meanwhile, traffic around the secure zone had returned to its usual, snarled state.

Around the blast site, damaged structures could be seen with their windows blown out, and even concrete blast walls had been sent tumbling by the powerful explosion. An Afghan official on the scene told CNN that German and American forensics teams were at the scene gathering evidence.

Protesters chant anti-Taliban and anti-ISIS slogans Thursday near the blast site.

Near a security checkpoint, about 40 protesters chanted anti-ISIS slogans and called for "death" to the Taliban.

Protest organizer Kanishka Nasiry showed CNN a baby's shoe that he said he found on the street by the blast site. He lamented that the world pays less attention to what happens in Afghanistan than elsewhere, even though innocent civilians die here too.

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Afghans point finger at Pakistan

Afghanistan's intelligence service, the National Directorate of Security, issued a statement attributing blame to the Haqqani Network, a Taliban-affiliated group in Pakistan. It alleged the group had received help from ISI, the Pakistani intelligence service.

However, Pakistani Foreign Ministry spokesman Nafees Zakaria rejected what he called "baseless allegations," saying the "accusatory approach is unhelpful towards efforts for peace."

Zakaria insisted that "Pakistan has highest stakes in peace and stability in Afghanistan," and said it was "disappointing that some elements, who have no interest in peace in Afghanistan and want to damage Afghan-Pakistan relations, have been maligning Pakistan for their own agenda."

The Haqqani Network has not responded to the accusation from Afghanistan's intelligence service, nor claimed responsibility for the attack.

The Taliban have denied responsibility for the blast, and ISIS has remained silent on the issue.

An Afghan security officer is seen in Kabul on Thursday amid a heightened security presence.

As the nation grieved, Afghan President Ashraf Ghani extended his "deepest condolences" in a live televised address. "It was a brutal act which has caused our countrymen grief during the holy month of Ramadan," he said.

Reporting from Kabul on Thursday, CNN's Muhammad Lila said people were angry that so much money was spent by so many countries to safeguard Afghanistan's security and yet the attack still couldn't be stopped.

"The fact that this can happen in the country's capital, that a truck filled with so many explosives could just drive up and detonate. There's a lot of anger right now directed at officials," he said.

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Security issues

CNN Security Analyst Rick Francona said it was "not surprising" that the Haqqani Network was being blamed, having previously demonstrated its ability to carry out attacks of similar scale.

"What is surprising is the ability to get this far into a secured area. They didn't quite reach the gates of the green zone, but they got very close," said Francona.

"Not just the US, NATO has put billions of dollars into training and reorganizing the Afghan army ... I think we're seeing the results of the failure of that effort."

Photos: A suicide bomb attack targets Kabul's diplomatic zone Afghan security forces patrol the site of a deadly suicide bomb attack in Kabul, Afghanistan, on Wednesday, May 31. The blast struck near the German Embassy, according to Afghan officials. Hide Caption 1 of 14 Photos: A suicide bomb attack targets Kabul's diplomatic zone Hide Caption 2 of 14 Photos: A suicide bomb attack targets Kabul's diplomatic zone A wounded man is helped away from the scene of the attack, which struck in the midst of Kabul's morning rush hour. Hide Caption 3 of 14 Photos: A suicide bomb attack targets Kabul's diplomatic zone Women covered in blood stand dazed in the aftermath of the attack near Kabul's highly secure diplomatic area. Hide Caption 4 of 14 Photos: A suicide bomb attack targets Kabul's diplomatic zone An injured man receives aid following the attack. Hide Caption 5 of 14 Photos: A suicide bomb attack targets Kabul's diplomatic zone Bystanders help evacuate people from the area of the explosion. Hide Caption 6 of 14 Photos: A suicide bomb attack targets Kabul's diplomatic zone Security forces gather near the site of the attack. Hide Caption 7 of 14 Photos: A suicide bomb attack targets Kabul's diplomatic zone People help an injured man following the attack. Hide Caption 8 of 14 Photos: A suicide bomb attack targets Kabul's diplomatic zone Victims' bodies are placed in the back of a police truck at a hospital in Kabul. Hide Caption 9 of 14 Photos: A suicide bomb attack targets Kabul's diplomatic zone Office workers leave the site of the suicide attack. German Foreign Minister Sigmar Gabriel said the attack was "aimed at civilians and those who are in Afghanistan to work with the people there for a better future of the country." Hide Caption 10 of 14 Photos: A suicide bomb attack targets Kabul's diplomatic zone German and Afghan authorities inspect the scene of the blast. German Foreign Minister Sigmar Gabriel said the attack was in the "immediate vicinity" of the nation's embassy. "In the attack, officials of the German Embassy were also injured. In the meantime, all employees are safe," Gabriel said. Hide Caption 11 of 14 Photos: A suicide bomb attack targets Kabul's diplomatic zone Volunteers carry the body of a victim to the Wazir Akbar Khan Hospital in Kabul. Hide Caption 12 of 14 Photos: A suicide bomb attack targets Kabul's diplomatic zone A mangled vehicle is lifted out of the wreckage after the explosion. Hide Caption 13 of 14 Photos: A suicide bomb attack targets Kabul's diplomatic zone A man wounded in the car bomb attack is treated at a hospital in Kabul. Hide Caption 14 of 14

Afghanistan's ambassador to the UK, Said Tayeb Jawad, told CNN's Clarissa Ward that the country's security agencies had intercepted "many similar attacks," including one a few days ago.

"The indications are that (Wednesday's attack) was carried out by terrorists outside Afghanistan. Definitely the logistical work that is needed is not possible unless they get the financial and logistical support in Pakistan," Jawad said.

"We are trying to do everything possible to reach out to Pakistan to make them understand that supporting terrorist groups is not going to benefit Afghanistan or Pakistan. So far our effort has not been fruitful," he added.

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CNN International Diplomatic Editor Nic Robertson said the Haqqani Network, which operates across a lawless area extending from near Khost in southeastern Afghanistan into Pakistan, is widely understood to be funded by ISI, although Pakistan denies this.

The network is ostensibly part of the Afghan Taliban but was the only group that didn't pledge full allegiance to late Taliban leader Mullah Omar, he said. It's the most militant part of the Taliban although its interests are not so much ideological as financial, such as smuggling across the border, or concerned with maintaining power.

Some of the biggest attacks in the past have been the work of the group, now headed by a second generation of jihadi leaders from the Haqqani family, he said.

Embassies, companies hit

Wednesday's devastating explosion happened close to Western embassies, government institutions and various residencies of high-ranking officials.

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Eleven US citizens, assigned to the US Embassy as contractors, were injured in the explosion while at Camp Eggers, a US facility across the street from the German Embassy. Nine Afghan security personnel working for the United States were killed.

The BBC said driver Mohammed Nazir had died in the blast. Four BBC journalists were injured, but their injuries are not thought to be life-threatening, according to a BBC World Service statement.

TOLO news employee Aziz Navin, 22, was killed on his way to work, the news agency reported

German Foreign Minister Sigmar Gabriel said the bombing was in the "immediate vicinity" of its embassy. The French and Canadian embassies were also damaged in the attack, as were the offices of broadcaster 1TV Afghanistan.