"We also reiterate our condemnation of terrorism in all its forms," a foreign ministry statement said.
"We extend our deepest condolences to the bereaved families and offer best prayers for the speediest recovery of those injured," it said.
The Taliban insurgent group claimed responsibility for the attack.
The attackers struck the restaurant frequently visited by foreigners at a busy dining time, detonating bomb and firing indiscriminately at the people.
At least 13 foreigners and eight Afghans lost their lives, Kabul police spokesman Hashmatullah Stanikzai said.
Officials said UN members and senior International Monetary Fund (IMF)'s official Wabel Abdallah were among those killed in the attack.
IMF Managing Director Christine Lagarde said in a statement Abdallah had been leading the fund's office in Kabul since 2008.