Afghanistan ? Marines moving by land from the north linked up with U.S. units that have faced nearly constant Taliban attack in the four days since they were dropped by helicopter into this insurgent stronghold in southern Afghanistan.

Also Tuesday, U.S. artillery fired nonlethal smoke rounds to disperse Taliban fighters in Marjah — the first time cannons have been used in the fight to drive the militants from their logistical and opium poppy-smuggling base. Commanders refused a Marine request to fire deadly high-explosive rounds because the unit on the ground could not be sure civilians weren’t at risk.