U.S. Rangers Seize Aidid’s Top Assistant : Somalia: The raid comes after militiamen attack a U.N. convoy of Pakistanis, killing three and injuring seven.

U.S. Army Rangers hunting for fugitive warlord Mohammed Farah Aidid scored their first major success Tuesday by capturing his chief aide.

United Nations military spokesman Maj. David B. Stockwell called Osman Atto’s arrest “a significant milestone in dismantling the Aidid militia.” The militia is blamed for killing more than 50 U.N. peacekeepers and plaguing the effort to rescue Somalia from famine and civil war.

About 50 helicopter-borne elite Rangers took part in the operation. They slithered down ropes to seize Atto and three other Aidid supporters in a building near Digfer Hospital, an area that officials say has been used to lob mortar rounds into U.N. headquarters in Somalia.

Militiamen opened fire on the helicopters and troops with small arms and at least a dozen rocket-propelled grenades. No U.S. forces were wounded, Stockwell said.

The 20-minute raid Tuesday follows a series of increasingly brazen attacks on U.N. forces. Earlier in the day, Somali militiamen opened fire on an armored convoy of Pakistani peacekeepers, killing three and wounding seven, two of them seriously.

Stockwell described Atto, a wealthy Somali businessman, as the principal adviser and chief financier to Aidid. Somalis consider the middle-aged Atto to be Aidid’s No. 2 man.

The Rangers were sent to Somalia to capture Aidid. The elite troops have twice bungled their efforts--accidentally raiding a U.N. office and arresting supporters of Aidid’s chief enemy, Ali Mahdi Mohamed.

After Atto’s capture, Aidid’s supporters threatened to attack U.N. installations in Mogadishu if he was not freed within four hours. That deadline passed without an attack, but the militia then said it would strike today.

Stockwell said U.N. forces were taking extra security measures.

“We understand the importance of detaining him and the potential emotional outburst that may follow this,” he said.

One of those arrested with Atto was shot in the leg when he tried to resist arrest, Stockwell said. He said the man had an AK-47 assault rifle.

Stockwell said some militiamen were killed in the fighting but no civilian casualties were reported. An unconfirmed Somali report said 13 in Aidid’s forces were dead and 29 wounded.

Atto’s legal situation was unclear. Stockwell said he was arrested under U.N. Security Council Resolution 837, which calls for the punishment of those responsible for the deaths of 24 Pakistani peacekeepers in a June 5 ambush.

U.N. officials ordered Aidid’s arrest after that attack and offered a $25,000 reward for his capture.

More than 27,000 soldiers from 28 nations are involved in a U.N. operation to help Somalia recover from its famine and civil war. But the troops have wound up in almost daily battles with Aidid’s militiamen.

Farouk Mawlawi, a civilian U.N. spokesman, said Atto was being held under “administrative detention,” but it was unclear how long he could be jailed without seeing a lawyer. Mawlawi said U.N. officials in New York would have to decide where and how Atto would be tried.