(2) to arrest any alien who in his presence or view is entering or attempting to enter the United States in violation of any law or regulation made in pursuance of law regulating the admission, exclusion, expulsion, or removal of aliens, or to arrest any alien
in the United States, if he has reason to believe that
the alien so arrested is
in the United States in violation of any such law or regulation and is likely to escape before a warrant can be obtained for his arrest, but the alien arreste