; or (2) against the Secretary concerned if the Secretary concerned failed to perform any act or duty under this Act, or to issue any regulation under this Act, required by this Act. (b) District court jurisdiction (1) In general The United States district courts shall have jurisdiction over an action brought under this section, without regard to the amount in controversy or the citizenship of the parties, including actions brought to apply any civil penalty under this Act. (2) Agency action unreasonably delayed The United States district courts shall have jurisdiction to compel agency action unreasonably delayed, except that an action to compel agency action reviewable under section 505 may only be filed in a United States district court within the circuit in which such action would be reviewable under section 505. (c) Exceptions (1) Notice No action may be commenced under subsection (a) before the end of the 60-day period beginning on the date the plaintiff has given notice in writing of such alleged violation to the alleged violator and the Secretary concerned, except that any such action may be brought immediately after such notification if the violation complained of constitutes an imminent threat to the environment or to the health or safety of the public or to property eligible for listing on the National Register of Historic Places. (2) Ongoing litigation No action may be brought against any person other than the Secretary concerned under subsection (a)(1) if the Secretary concerned has commenced and is diligently prosecuting a civil or criminal action in a court of the United States to require compliance. (3) Exception No action may be commenced under subsection (a)(2) against the Secretary concerned to review any regulation issued, or any permit issued or denied, by the Secretary concerned if such regulation or permit issuance or denial is judicially reviewable under section 505 or under any other provision of law at any time after such issuance or denial is final. (d) Venue Venue of all actions brought