"During the night of 9 to 10 November, a soldier serving the 22nd motorised infantry battalion was cruelly killed by a squad of terrorists," government spokesman Issa Tchiroma Bakary told AFP.
The incident took place in the southwestern administrative region, one of two where unrest has broken out among Cameroon's anglophone minority. The other three soldiers were killed in the northwest.
French-speaking Cameroon has a large anglophone community which comprises about a fifth of its 22 million population.
Many English speakers say they suffer economic inequality and discrimination at the hands of the francophone majority, particularly in education and justice.
Tchiroma said the soldier had been guarding a bridge on the border with Nigeria at Akwem, not far from the city of Mamfe.
On October 1, a breakaway movement issued a symbolic declaration of independence for their putative state of "Ambazonia," led by Sisiku Ayuk.
On Thursday Ayuk used his Twitter account to condemn the earlier killings and denied his movement's responsibility.
President Paul Biya fiercely opposes secession or a return to Cameroon's former federal structure.
The agitation began at the end of 2016 but has met with a crackdown that has alarmed human-rights watchdogs.
At least 14 people have died in clashes, as well as five prisoners who were killed while trying to escape jail, according to a toll compiled by AFP.
International monitors, in contrast, say at least 20 and possibly 40 people have been killed in clashes since late September.