KABUL, Afghanistan -- The Afghan government banned warlords Sunday from taking part in politics, a move that would prevent some of the country's top leaders from participating in next year's pivotal elections.

The new law is seen as crucial to helping the country become a stable democracy, as Afghanistan has long been dominated by private militias whose rivalry kept the country at war for 23 years.

"Nobody with armed forces behind them can continue their political activities," Justice Minister Abdulrahim Karimi told a news conference Sunday.

The law, if enforced, is likely to affect several of the nation's leaders. The Northern Alliance, which supported Hamid Karzai in becoming president after the ouster of the Taliban in late 2001, is a collection of warlords -- many of them provincial governors or national politicians.

There are also warlords in Karzai's Cabinet. Defense Minister Mohammed Fahim, for example, maintains one of the largest private armies, and many of his soldiers are based in the capital, Kabul.

Fahim is an ethnic Tajik and seen as a potential political rival to Karzai, an ethnic Pashtun. It was not clear how the government, which has little power outside Kabul, would enforce the law.

Approved by the government Saturday, the law also dictates that a political party must have at least 700 members before it can be registered.

"This is another important step toward democracy," Karimi said.

The measure comes as political leaders start to position themselves for general elections in June. Karzai's government is a coalition of several ethnic groups and political factions; it will be a major challenge for him to keep it together.

Fahim and other members of the Northern Alliance met earlier this month in the capital while Karzai was overseas, and are believed to have discussed withdrawing their support for the president.

Karzai's administration appears to be becoming less tolerant of criticism as the polls draw closer. On Saturday, it shut down the country's second most-popular newspaper, state-run Armon Mali, apparently after it ran a series of critical articles.

Deputy Information Minister Abdul Hamid Mubarrez denied the government closed the newspaper to end the criticism and said it was because there were now enough privately run papers for the public to read.