KABUL, Aug. 25 (Xinhua) -- Afghan President Ashraf Ghani on Saturday appointed the Afghan ambassador to the United States as his new national security advisor, a presidential spokesman said.

Hamdullah Mohib will replace Mohammad Hanif Atmar, who resigned earlier Saturday, citing serious differences with leadership of the government over issues related to security, peace, electoral process, national unity and consensus as well as regional and international relations, spokesman Haroon Chakhansuri tweeted.

The resignation came amid deteriorating security and increased terrorist attacks in the war-torn country.

Islamic State (IS) militants launched a mortar attack on the Presidential Palace, the Defense Ministry building and nearby diplomatic district in Kabul on Tuesday.

Scores of security forces and civilians were either killed or wounded in Ghazni city, capital of eastern Ghazni province after Taliban militants captured the city earlier this month.