A Massachusetts Air National Guardsman accused of posting dozens of secret intelligence reports and other sensitive documents on a social media server is expected to plead guilty in federal court on Monday.

Federal prosecutors told a judge on Thursday that the defendant, Jack Teixeira, intended to change his plea after initially pleading not guilty. A person familiar with the proceedings also said that the airman had agreed to a plea deal.

Airman Teixeira is charged with mishandling national defense information and classified documents. Prosecutors say he took the material off computers at an intelligence unit at an air base in Cape Cod, sharing them with online friends in an effort to impress them.

Among the secrets disclosed was information on the provision and delivery of military equipment to Ukraine and a highly sensitive report on Russian and Ukrainian troop movements. Officials said the disclosures about the troop movements might have compromised how American intelligence gathered the information and from whom.

Airman Teixeira posted the information online over a period of months.

This is a developing story. Check back for updates.

Glenn Thrush contributed reporting.