II. Definitions and cross-cutting issues reasonable grounds for the refusal (reasonable grounds would include, for example, existence of an outstanding detention order related to a criminal investigation). (iii) Persons with undetermined nationality are considered as such when a preliminary review has not determined whether they possess a nationality or are stateless. Such cases arise in a wide range of contexts and, in most instances, can be resolved through existing State procedures for confirmation of nationality and provision of related identity documentation. These persons can fall within UNHCR’s statelessness mandate if they: — lack proof of possession of any nationality; and — have links to more than one State on the basis of birth, descent, marriage or habitual residence; or — are perceived and treated by the authorities in the State of residence as possessing links which give rise to a claim of nationality of another State on the basis of such elements as historic ties, race, ethnicity, language or religion. Persons at risk of statelessness is another frequently used term, yet there is no formal definition in international law specifying what “at risk of statelessness” means. However, from various sources it can be concluded that persons are at risk of statelessness when they have difficulties proving that they have relevant links to a State. This can happen, for example, when a person does not have a birth certificate or identity documents. The following categories of persons, which are not mutually exclusive, may be at risk of statelessness, in particular, in the absence of birth registration or identity documentation: — migrant populations for which difficulties to prove identity and nationality affect two or more generations; — persons living in border areas, whose births are not registered in either country; — national or ethnic minorities who have perceived or actual ties with other countries; 14