WASHINGTON — Nearly 300 American armed forces are being positioned in and around Iraq to help secure U.S. assets as President Barack Obama nears a decision on an array of options for combating fast-moving Islamic insurgents, including airstrikes or special forces.

The U.S. and Iran also held an initial discussion on how the longtime foes might cooperate to ease the threat from the al-Qaida-linked militants that have swept through Iraq. Still, the White House ruled out the possibility that Washington and Tehran might coordinate military operations in Iraq.