US Defense Secretary Jim Mattis arrived in Afghanistan on an unannounced visit today, an American defence official confirmed, hours after his Afghan counterpart resigned over a deadly Taliban attack.

Mattis, making his first visit to Afghanistan as Pentagon chief, was due to meet top officials including President Ashraf Ghani less than two weeks after the US dropped its largest non-nuclear bomb on Islamic State hideouts in the country's east.

He arrived as embattled Afghan security forces faced chaos with the resignations of defence minister Abdullah Habibi and army chief Qadam Shah Shaheem. The resignations, announced in a terse one-line statement from the presidential palace, came amid fury over the Taliban assault on an army base outside the northern city of Mazar-i- Sharif on Friday.