"We want to collect ourselves as a team and support each other in processing this incomprehensible act and finding our two unaccounted for colleagues", she added.
In a report on its work in Afghanistan a year ago, the ICRC said high levels of insecurity in the country had made it hard to provide aid.
The Taliban, the largest militant group in Afghanistan, said they were not behind the attack.
"Nothing can justify the murder of our colleagues and dear friends".
ICRC's director of operations Dominik Stillhar said the operations of the global charity are on hold at the moment after Wednesday's attack, Khaama Press reported on Thursday.
The workers were shot in the Qush Tepa area, the provincial governor said.
Besides determining the operational impact of the attack, Stillhart said ICRC would pause its programs out of respect for the slain aid workers.
A search operation was underway to find two charity workers who were still missing late on Wednesday night. The local staff were immediately released.
The organisation said its convoy - three drivers and five field officers - were on their way to deliver livestock materials to communities affected by recent heavy snow storms when it was attacked by unknown armed men.
One of Switzerland's most iconic humanitarian aid organisations suffered its worst attack in 20 years, bringing a temporary halt to its aid operations in Afghanistan..
In December 2016, gunmen in northern Afghanistan had abducted a Spanish ICRC employee, who was released a month later.
Since ISIS announced the creation of the Khorasan province of its so-called caliphate in Afghanistan and Pakistan in January 2015, the Sunni terror group has carved out footholds in the eastern province of Nangarhar, bordering Pakistan, as it competes with rivals the Taliban and al Qaeda for influence.
The terrorist organization claimed responsibility for Tuesday's deadly suicide bombing in Kabul, targeting mostly employees of the Afghan Supreme Court.