The four are two environment ministry workers, their guide and and a Cameroonian intern.
The Senegalese environment ministry said the three were on a mission to produce a report on the management of natural resources in Senegal.
“(They) are being held by police in Bafing in Gambia. After being contacted by the environment ministry, the relevant authorities are following up this unfortunate incident with our neighbour, the Gambia,” the ministry said, as reported by the AFP.
According to the AFP, a Senegalese security source said they were arrested while taking pictures of logs being stored on the Gambian side of the border.
It is believed there is an illegal timber trade carried out on Senegalese soil by Gambian loggers who sell to Chinese loggers.
Relations between the two countries become increasingly fractious as a dispute over custom duty continues. The Gambia in February increased the custom duty for Senegalese truckers from 4,000 CFA ($7) to 400,000 CFA ($700) per truck but the Senegalese protested leading to the closure of the border.
Edited: An earlier version of this story said the arrested people were three. We understand they are four not three. Apologies for the error.