A child stand near stairs outside his home on a hill top in Kabul on July 13, 2021. (SAJJAD HUSSAIN / AFP)

More Afghans are likely to flee their homes due to escalating violence, the UN refugee agency warned on Tuesday, as the Taliban take control of more territory in response to the withdrawal of US-led foreign forces.

"Afghanistan is on the brink of another humanitarian crisis. This can be avoided. This should be avoided," Babar Baloch, spokesman of the UN High Commissioner for Refugees (UNHCR), told a Geneva news briefing.

The number of civilian casualties has risen by 29 percent during the first quarter compared with 2020, the UN High Commissioner for Refugees said

"A failure to reach a peace agreement in Afghanistan and stem the current violence will lead to further displacement within the country, as well as to neighboring countries and beyond."

The UNHCR said an estimated 270,000 Afghans had been newly displaced inside the country since January, bringing the total population forced from their homes to more than 3.5 million.

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Those forced to flee blamed the security situation, incidents of extortion by non-state armed groups and improvised explosive devices (IEDs) on major roads, as well as a loss of income and interruptions to social services, Baloch said.

The number of civilian casualties has risen by 29 percent during the first quarter compared with 2020, the UNHCR said, citing figures from the UN Assistance Mission in Afghanistan.

"We urge the international community to step up support to the government and people of Afghanistan and its neighbors at this critical moment," Baloch said.

The US general leading the war in Afghanistan, Austin Miller, relinquished command at a ceremony in the capital, Kabul, on Monday and quietly left the country, a symbolic end to America's longest conflict.

US President Joe Biden has acknowledged that Afghanistan's future was far from certain but said the Afghan people must decide their own fate.

Meanwhile, the Taliban warned Turkey on Tuesday against plans to keep some troops in Afghanistan to run and guard Kabul's main airport after the withdrawal of foreign soldiers, calling the strategy "reprehensible" and warning of "consequences".

Ankara, which has offered to run and guard the airport in the capital after NATO withdraws, has been in talks with the United States on financial, political and logistical support.

Turkey has repeated that the airport must stay open to preserve diplomatic missions in Afghanistan, where a blast rocked Kabul on Tuesday and clashes have intensified across the country.

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"The Islamic Emirate of Afghanistan condemns this reprehensible decision," the Taliban said in a statement, referring to Turkey's plan.

"If Turkish officials fail to reconsider their decision and continue the occupation of our country, the Islamic Emirate... will take a stand against them."

In that case, the militant group added, the responsibility for consequences would fall on the shoulders of those who interfere.

The Taliban, who ruled Afghanistan with an iron fist from 1996 to 2001, have been fighting for 20 years to topple the Western-backed government in Kabul and reimpose Islamic rule.

Emboldened by the departure of foreign forces by a September target, they are making a fresh push to surround cities and gain territory.