Gambian police have arrested three workers carrying out an environmental study for the Senegalese government on their shared border, as relations between the two countries become increasingly fractious.

A Senegalese worker at the environment ministry, a Cameroonian intern and their Senegalese guide were arrested on Saturday near the border village of Niaming, the ministry said in a statement.

"(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 statement said.

The team's mission was to eventually produce a report on the management of national resources in Senegal, the ministry said.

However a Senegalese security source said the trio were arrested while talking pictures of logs being stored on the Gambian side, as disputes mount over a thriving illegal timber trade carried out on Senegalese soil by Gambian loggers.

The southern region of Casamance is particularly affected as it benefits from significant forest cover, and logging is often carried out with the support of local communities in this impoverished area.

The timber is then sold on to Chinese loggers when it is transported into the Gambia.

The dispute comes after the Gambia infuriated Senegalese truck drivers by increasing customs duty from 4,000 CFA ($7) to 400,000 CFA ($700) per truck without warning in early February.

The action prompted the west African regional bloc ECOWAS to dispatch a team to mediate after the border was effectively closed and a series of attempts at talks failed.

The Gambia has since announced it will lower tariffs back to their previous levels.