WASHINGTON -- Nine Afghan guards at the U.S. Embassy in Kabul were killed and 11 American contractors wounded in the massive suicide truck bomb attack that rocked the diplomatic quarter in Afghan capital on Wednesday, the State Department said. One other Afghan guard was reported missing.

None of the wounded Americans appears to have life-threatening injuries as a result of the attack in which Afghan officials say at least 90 people were killed and 400 were wounded.

Secretary of State Rex Tillerson condemned the attack, offering condolences to the families and friends of the victims and prayers for recovery of those wounded.

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"In the face of this senseless and cowardly act, the U.S. commitment to Afghanistan is unwavering; the United States stands with the government and the people of Afghanistan and will continue to support their efforts to achieve peace, security, and prosperity for their country," Tillerson said in a statement.

President Trump spoke with Afghan President Ashraf Ghani in the aftermath of the attack, which CBS News correspondent Debora Patta reports was one of the worst attacks Kabul has seen since the drawdown of foreign forces at the end of 2014.

An Afghan man reacts at the site of a blast in Kabul, Afghanistan May 31, 2017. Reuters

"I have been to many attacks, taken wounded people out of many blast sites, but I can say I have ever seen such a horrible attack as I saw this morning," ambulance driver Alef Ahmadzai told The Associated Press. "Everywhere was on fire and so many people were in critical condition."

There was no claim of responsibility for the attack, which came in the first week of the Muslim holy month of Ramadan.

Both the Taliban and the Islamic State of Iraq and Syria (ISIS) have staged large-scale attacks in the Afghan capital in the past.

The Taliban flatly denied any involvement in an email to news outlets and condemned all attacks against civilians.

The explosion occurred at the peak of Kabul's rush hour when roads are packed with worktime commuters, Patta reports.

The U.S. Embassy in Kabul warned American citizens to avoid the area of the blast and cancelled all its appointments for routine American Citizen Services for the day.

White House press secretary Sean Spicer said during today's press briefing that the U.S. Embassy will provide assistance and bring perpetrators to justice.

Relatives of Afghan victims mourn outside a hospital after a blast in Kabul, Afghanistan, on Wed., May 31, 2017. Reuters

In a statement, members of the United Nations Security Council condemned the attack, calling it cowardly and heinous.

"The members of the Security Council underlined the need to bring perpetrators, organizers, financiers and sponsors of these reprehensible acts of terrorism to justice," the statement said.

They reiterated that "any acts of terrorism are criminal and unjustifiable, regardless of their motivation, wherever, whenever and by whomsoever committed," according to the statement.

Last month, the Afghan Taliban announced the beginning of their spring offensive, promising to build their political base in the country while focusing military assaults on the international coalition and Afghan security forces.

U.S. and Afghan forces have been battling the Taliban insurgency for more than 15 years. The United States now has more than 8,000 troops in Afghanistan, training local forces and conducting counterterrorism operations. In the past year, they have largely concentrated on thwarting a surge of attacks by the Taliban, who have captured key districts, such as Helmand province, which U.S. and British troops had fought bitterly to return to the government.