Six Afghan employees of the International Committee of the Red Cross (ICRC) have been killed in an attack in the northern Afghan province of Jowzjan, officials say.

The international charity said on February 8 that another two ICRC workers remained unaccounted for.

"Devastated by this news out of #Afghanistan," ICRC President Peter Maurer said on Twitter. "My deepest condolences to the families of those killed -- and those still unaccounted for."

No one immediately claimed responsibility for the attack, but provincial Governor Mawlawi Lutfullah Azizi said suspected Islamic State (IS) gunmen were behind it.

Militants loyal to the IS group were "very active" in the area, he added.

Azizi also said the aid workers were in a convoy carrying supplies to areas hit by avalanches when they were attacked in the Qush Tepa district.

The Taliban, which frequently uses roadside bombs and suicide attacks to target officials and security forces across Afghanistan, denied involvement.

IS militants have made limited inroads in Afghanistan, but have carried out increasingly deadly attacks.

The killings come after a Spanish worker of the ICRC was abducted in northern Afghanistan in December and released less than a month later. The ICRC or Afghan officials did not say how he was freed or who was behind the abduction.

Also on February 8, the IS group claimed responsibility for a suicide attack that killed at least 20 people outside the Supreme Court in the capital, Kabul.

The bomber, identified as Abu Bakr Altajiki by the militants, detonated an explosive belt as court employees were leaving work in the evening of February 7.

White House spokesman Sean Spicer called the bombing a "cowardly attack" and said U.S. national security adviser Michael Flynn had phoned his Afghan counterpart, Mohammad Atmar, to "reaffirm our support to the Afghan government."

Elsewhere in Afghanistan, officials said a suicide bomber detonated his explosives at the gate of a district headquarters in the eastern province of Paktia, killing two civilians.

A guard was also wounded in the February 8 attack in Dand-e Patan district near the Pakistan border.

"The suicide bomber wanted to enter the district headquarters, but police identified and asked him to stop," provincial police chief Qadir Gul Zadran said. "The bomber immediately detonated his explosives."

No group has yet claimed responsibility for that attack.

With reporting by dpa, AP, Reuters, and AFP