Afghanistan's interior minister, Ali Ahmad Jalali, says he will step down to resume his academic career in the United States. There is speculation that Mr. Jalali opposed Afghan President Hamid Karzai's decision to bring factional leaders into Afghanistan's government.

Mr. Jalali announced his decision during a television interview broadcast in Afghanistan. He said a primary reason for his departure was a desire to resume his academic and scientific research.

Mr. Jalali spent more than two decades in the United States, where he worked as a political analyst and journalist for the Voice of America. He also wrote academic articles on such subjects as the Soviet-Afghan War of the 1980's.

The interior minister has scheduled a press conference for Wednesday to discuss his resignation.

President Hamid Karzai's office is denying reports that Mr. Jalali's decision was motivated by disagreement with the president's policies regarding regional leaders joining the central government.

Government spokesman Karim Rahimi briefly addressed the resignation during a regularly scheduled press conference.

Mr. Rahimi says the minister's decision was a personal one and was not politically motivated.

Mr. Jalali joined Mr. Karzai's cabinet in 2003, and quickly emerged as one of the president's best known and most respected advisors. As minister of the interior he oversaw efforts to disarm former militants and combat Afghanistan's booming drug industry.

But there has been growing speculation of a political rift between the two men.

Analysts say he opposed Mr. Karzai's decision to appoint several men with strong regional constituencies to provincial posts in the new government. Mr. Jalali frequently cited concerns about former warlords and ethnic leaders, questioning whether they would ever fully support the central government.

The outspoken minister has also accused some government officials of supporting regional drug lords.

Afghanistan produces up to 90 percent of the world's opium supply. Mr. Jalali has identified drugs and factionalism as two of the country's greatest challenges.

Aides to Mr. Jalali say he is expected to return to the United States after his resignation becomes effective.