Consonant Clustering
Two or more consonant sounds may appear sequentially linked or clustered as either identical consonants or homorganic consonants which differ slightly in the manner of articulation—as when the first consonant is a fricative and the second is a stop.
In some languages a syllable-initial homorganic sequence of a stop and a nasal is quite uncontroversially treated as a sequence of two separate segments; and the separate status of the stop and the nasal is quite clear. In Russian, the stop + nasal sequences are just one of the possible types amongst many different syllable-initial consonant sequences which occur. In English, nasal + stop sequences within a morpheme must be homorganic.
Read more about this topic: Homorganic Consonants