GENEVA -- A crisis of huge proportions is brewing in Mali that could spread throughout the nine-nation Sahel region of northern Africa and beyond due to insufficient humanitarian aid for millions of people, top UN and U.S. officials said Friday.

Mali recently experienced a coup that emboldened rebels to seize the country's north. Islamist and other insurgent rebel factions have since been fighting each other as they try to keep ahold of northern Mali. The violence, and the imposition of harsh Islamic law in some areas, has forced many residents to flee their homes.

The officials warned that widespread hunger, displacement, insecurity, political unrest and other factors in Mali are putting countless lives at risk -- and setting the stage for a global headache.

"There is a very serious threat for peace and security, not only for the whole region but, in my opinion, with global implications," UN High Commissioner for Refugees Antonio Guterres told reporters at the UN in Geneva. "We are witnessing in the Sahel a dramatic humanitarian situation."

Guterres appeared a press conference beside U.S. Assistant Secretary of State Anne Richard, who oversees population, refugees and migration. They had just returned from a trip to visit Malian refugees in Burkina Faso.

Guterres said 260,000 Malian refugees have fled for neighbouring Mauritania, Niger and Burkina Faso, which have kept their borders open and shared their food supplies despite the dire hunger crisis they face within their own nations. Some 200,000 people also have been displaced within Mali, facing dire conditions.

The UN humanitarian office says 18 million people already face severe hunger and malnutrition in the Sahel region. In Mali, many of those in need are beyond the reach of aid workers, the two officials said.

"The United States is very concerned about the crisis, and we're also concerned that's there not sufficient resources going to it," said Richard, adding the U.S. has contributed $355 million of aid and food to countries in the Sahel, including $34.5 million for refugees.

A group of middle-ranking soldiers toppled Mali's democratically elected president in March. After international pressure, they allowed an interim president to be named in April. But in May, that interim leader, Dioncounda Traore, was beaten up by a group of protesters, and left the country for medical treatment. He returned last week.

The initial coup gave insurgents in Mali an opening. Ethnic Tuareg rebels seeking secession took control of the country's north -- an area larger than France -- but were driven out in June by extremist Islamists with links to al-Qaida who vowed to introduce an ultra-strict interpretation of Islamic law.

Guterres said the threat goes "far beyond northern Mali" partly because many of the heavily armed fighters there have come from Libya, where they had been in the army and militias that supported the late Libyan dictator Moammar Gadhafi, and others have come from Nigeria, Somalia and Afghanistan.

The crisis in Mali could become conflated with the unrest in Sudan-South Sudan, Somalia and even Yemen, he said.

"So if proper humanitarian assistance is not provided, and if a political solution is not found, the risk of this conflict to go far beyond Mali is, in my opinion, enormous," Guterres said. "And the implications are very serious for the whole region. Let's not forget that many of the states of this region are very fragile."