Abubacar was arrested while interviewing people fleeing attacks in the northern province of Cape Delgado, and has been in detention without trial for over three months, according to CPJ reporting.
He is being held in Mieze prison in Pemba and is being denied visits by his family, according to the joint statement.
Abubacar is among this month's "10 Most Urgent" cases of journalists under attack worldwide, according to the One Free Press Coalition, of which CPJ is a partner organisation.
The joint statement, issued on Mozambique's National Journalists' Day, can be read here.