BAGHDAD — In agreeing to cooperate to clear Islamic State forces out of a 60-mile-long strip of northern Syria along the Turkish border, the United States and Turkey have taken a major step toward increasing pressure on the militant group and easing their differences on the Syrian conflict.

The Obama administration, whose top priority is battling the Islamic State, also known as ISIS or ISIL, would get to use Turkish air bases to attack the militants on a new front and has won a new commitment from Turkey to try to shut off some of the group’s most important supply lines.

Turkey, whose primary goal has long been to oust President Bashar al-Assad of Syria, would get a new degree of security along its border — and in the process, keep a Syrian-based Kurdish militia force that it considers a threat from making inroads to the area.

But when it comes to carrying out the agreement, which was reached over the weekend and was described by four senior American officials, significant complications remain.