US President Donald Trump has said the Taliban could "possibly" overrun the United States-backed Afghan government after foreign troops withdraw from the country as part of a deal signed last week.

"Countries have to take care of themselves," Trump told reporters at the White House on Friday. "You can only hold someone's hand for so long."

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The US-Taliban deal signed in Qatar's capital last week would see US and NATO forces completely withdraw over a 14-month timeline to end the 18-year-long Afghanistan war.

Asked if the Taliban could eventually seize power from the current US-backed government, Trump said it is "not supposed to happen that way but it possibly will".

"We can't be there for the next 20 years. We've been there for 20 years and we've been protecting the country but we can't be there for the next - eventually, they're going to have to protect themselves," he said.

Trump, who on Tuesday had a "good talk" during a phone call with a senior Taliban leader, added he did not know if the Afghan government had the ability to defend itself from fighters after foreign forces pull out.

"I don't know. I can't answer that question," he said. "We'll have to see what happens."

Trump's statement came hours after nearly 30 people were killed in capital Kabul during an attack claimed by the ISIL (ISIS) group.

It was the deadliest attack in Afghanistan since the signing of the US-Taliban peace deal on February 29.

Intra-Afghan talks

The US-Taliban deal also included three other main conditions: a permanent and comprehensive ceasefire, a Taliban pledge that Afghan soil would not be used as a launchpad to threaten US security, and that intra-Afghan negotiations would be launched by March 10.

The intra-Afghan talks will be consequential to the future of the country as Afghan leaders and activists will sit face-to-face with the Taliban to chart a course for peace in the country.

Meanwhile, the much-anticipated deal has been met with both hope and scepticism in Afghanistan.

The Taliban held power in the South Asian country of 35 million from 1996 to 2001 and enforced a strict interpretation of Islamic law that was condemned by the international community.

Women were banned from working or studying under the Taliban rule, with three million girls returning to school following their government's toppling in 2001.

Many Afghans remain apprehensive over what the US-Taliban deal could mean for the future of women's education and empowerment in the country.