(Reuters) - More Afghans are likely to flee their homes due to escalating violence, the U.N. refugee agency warned on Tuesday, as the Taliban take control of more territory in response to the withdrawal of U.S.-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 U.N. High Commissioner for Refugees (UNHCR), told a Geneva news briefing.

       "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 neighbouring 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.

       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% during the first quarter compared with 2020, the UNHCR said, citing figures from the U.N. Assistance Mission in Afghanistan.

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

       The U.S. 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.

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

       (Reporting by Emma Thomasson; Editing by Robert Birsel)