Generally, foreign pensions do not qualify as retirement plans as defined in the US Internal Revenue Code (normally under Sec. 401). Therefore, a foreign pension account is generally treated as a foreign trust for US income tax purposes.

As a Foreign Trust, the Trustee generally has a duty to report information to any US Beneficiary (if there is one) on a Form 3520-A.  The Form 3520-A is purely a disclosure form and does not have any direct tax liability deriving from it; however, there are potential penalties for failing to provide it.

A US beneficiary of a foreign trust must generally report this information to the IRS on a Form 3520, as well as properly reporting any income on their Form 1040 or equivalent.