U.S. government agents have arrested two men and detained two others as part of an ongoing terrorism investigation in the western U.S. state of California.

One of those arrested, 22-year-old Hamid Hayat, is accused of training at an al-Qaida camp in Pakistan and then lying about it to FBI agents.

His father, Umer Hayat, is charged with lying about and financing his son's alleged terrorist activity.

The Los Angeles Times newspaper quotes a family member as denying the charges.

The two men made brief appearances in a U.S. district court on Tuesday. Both are U.S. citizens who live in the town of Lodi.

Media reports say as part of the investigation, federal agents have also detained two local Islamic leaders, Muhammed Adil Khan and Shabbir Ahmed. Both are being held for alleged immigration violations.