Part II
Extradition
CHAPTER I
Extradition from Portugal
Section II
Extradition procedure
Article 51
Introductory decision and arrest of the person claimed
3. If the case should proceed, the warrant of arrest of the person claimed shall be delivered to the public prosecutor who must promote its execution.
4. Should additional information be required, the competent authorities shall be instructed to keep the person claimed under surveillance, unless it is deemed necessary immediately to place that person under arrest on grounds that there are serious reasons for believing that the request will proceed.
Arrest for ICC proceedings - obligation
EDIT.