BRUSSELS, Belgium — NATO foreign ministers approved plans Thursday to send up to 6,000 troops into southern Afghanistan, a major expansion of the alliance's security mission in some of the most dangerous parts of the country.

The deployment next year of mostly European and Canadian troops will free up U.S. forces to focus on counter-insurgency operations against Taliban and al-Qaida fighters in Afghanistan's volatile south and east.

"We have today agreed to move NATO's support for peace and security in Afghanistan to a new level,'' the ministers said in a statement.

NATO's expansion should allow the United States to scale back its 18,000-member military presence almost five years after it invaded the country following the Sept. 11 attacks on New York and Washington. The Pentagon, however, has yet to say how many troops it will withdraw.

The plans give the NATO troops a stronger self-defence mandate, guarantee support from U.S. combat troops if they face a serious attack and set out rules for handling detainees -- all issues that have concerned some European allies mulling participation in the expanded force.

Ministers also agreed to a request from Afghan President Hamid Karzai to develop increased support in developing his country's fledgling security forces.

NATO Secretary General Jaap de Hoop Scheffer appealed for other international organizations to match the alliance's commitment to Afghanistan's security by doing more to help rebuild the country's economy.

"We are committed to stay the course,'' he told ministers. "But we are not working in a void there. Other international actors should stay equally committed.''

The European Union, the United Nations and the G8 group of the major world economic powers should join NATO at a conference planned for late January in London to relaunch development efforts, de Hoop Scheffer's spokesman, James Appathurai said. "The alliance cannot do everything,'' Appathurai told a news conference.

The military expansion will enlarge NATO's presence to about 16,000 troops and make it responsible for security in about three-quarters of the country. The separate U.S.-led combat force will keep the lead role in the eastern sector where Taliban holdouts have been most active.

NATO troops are scheduled to start moving into southern Afghanistan around May. Britain will play a lead role in the region, running a headquarters in Kandahar. NATO units led by troops from Canada, the Netherlands, Britain and the United States are expected to fan out into four southern provinces. Germany will lead NATO forces in the north and Italy in the west.