United Nations High Commissioner for Refugees Mr Ruud Lubbers arrived in Pakistan today to review operations ahead of a possible large-scale influx of Afghans.
The visit, his second to the region in six months, comes amid reports from Afghan refugees that the Taliban and opposition Northern Alliance are trying to force men to fight.
Thousands of Afghans are massed on the Afghan side of the border near the Baluchistan border checkpoint of Chaman, hoping that Pakistan will open its frontiers.
Most have fled 21 days of bombing of Kandahar, the stronghold of Taliban leader Mullah Mohammad Omar, and surrounding areas, in the US-led campaign to punish Afghanistan's hardline Taliban and their guest , Saudi-born militant Osama bin Laden.
The UNHCR, which fears up to 1.5 million Afghans could flee, has called for surrounding states - Pakistan, Iran, Tajikistan, Turkmenistan and Uzbekistan - to admit people fleeing starvation and the US-led bombing campaign.
Earlier, UN spokesman Mr Kris Janowski told a news briefing that many of the refugees crossing at Chaman have told UNHCR that they fear being forced to fight, either for the Taliban or their opponents.
Chaman is some 100 km southeast of the Taliban stronghold of Kandahar.
Pakistan and Iran, which already host some 3.5 million Afghan refugees, have officially closed their borders, but refugees are still reaching the countries. Tajikistan, Turkmenistan and Uzbekistan have also closed their frontiers.