Hundreds of people linked to a hard-line Islamic group have been arrested in Kabul in connection with an apparent plot to overthrow the government of interim Prime Minister Hamid Karzai, Afghan officials said Thursday.

The plot, the most serious threat yet to Karzai's fledgling administration, included plans to set off bombs throughout the capital, said Gen. Din Muhammad Jurat, the director general for security at the Interior Ministry. He said most of those arrested were members of Hezb-e-Islami, a hard-line Islamic group headed by former prime minister Gulbuddin Hekmatyar.

"They wanted to launch a coup d'etat against the government," said Mohammed Naseer, the security director at the Kabul governor's office. He said the plotters also wanted to disrupt the loya jirga, a political gathering planned for June to select a new Afghan government.

About 350 people had been arrested, most in the past three days, Naseer said.

International Security Assistance Force peacekeepers were not involved in the operations, but were tipped off of the raids in advance so they could stay clear of the area, said Lt. Col. Neal Peckham, a force spokesman.

Peckham said weapons had been found and that those arrested also included Pakistani members of another militant group, the Jamiat-e-Islami, the main supporter of Hekmatyar in Pakistan.

Some 600 people were rounded up in the raids, and 250 released, said another Western official in Kabul, speaking on condition of anonymity. Ten were being held on suspicion of serious offenses, including terrorism, the official said.

The roundups could heighten tensions between Pashtuns, Afghanistan's largest ethnic group, and the northern alliance, which is dominated by ethnic Tajiks and which controls the interior and other key ministries. Hekmatyar's following is largely Pashtun.

Afghan police on Monday raided the home of Hekmatyar's one-time aide, Wahidullah Sabaun, but there was some confusion Thursday over his whereabouts. Jurat and Naseer said Sabaun was among those arrested in the sweep, but Peckham said the man was still at large.

Sabaun was once the military chief of Hezb-e-Islami and served as Afghanistan's defense minister in 1995 when Hekmatyar became prime minister under President Burhanuddin Rabbani. When the Taliban took over the country in 1996, Sabaun allied himself with the northern alliance resistance.

Hekmatyar has been a vocal opponent of Karzai and of U.S. presence on Afghan soil, but last month his deputy, Jumma Khan Hamdard, said the party was ready to cooperate with the interim administration.

A senior leader of Hezb-e-Islami, Qutbuddin Hilal, said those arrested were former members of the group.

"There is no truth in these reports that our men are being arrested," Hilal said.

Ruthless power struggles among Hekmatyar's forces and northern alliance factions devastated much of Kabul during the early 1990s, with 50,000 people, mostly civilians, killed, according to the International Red Cross.

Hekmatyar fled to Iran after the Taliban took the capital in 1996, although the Iranian government recently closed his offices in Tehran and his whereabouts are unknown.

Naseer said the men arrested "were linked to both Al Qaeda and Gulbuddin Hekmatyar," but he refused to elaborate. He said most of those arrested were living in the upscale Wazir Akhbar Khan and Old Makrorayan neighborhoods of central Kabul.

Jurat said the interim administration had documents and strong evidence that linked Hekmatyar to the plot, but made no mention of Al Qaeda, Usama bin Laden's terrorist network.