A U.S. federal judge authorized the seizure of Citgo Petroleum Corp. to satisfy a Venezuelan government debt, a ruling that could set off a scramble among Venezuela’s many unpaid creditors to wrest control of its only obviously seizable U.S. asset.

Judge Leonard P. Stark of the U.S. District Court in Wilmington, Del., issued the ruling Thursday. However, his full opinion, which could include conditions or impose further legal hurdles, was sealed. A redacted version is expected to be available at a later date.

The...