U.S. diplomats at the embassy in Kabul warned in a classified memo to Secretary of State Antony Blinken and the department's leadership last month that the Afghan government was at risk of collapse as the Taliban offensive swept across the country, a source familiar with the memo confirmed to ABC News.

The dissent cable, as such memos are called at the agency, was sent on July 13 and was immediately brought to Blinken's attention, the source said.