Nearly 70 Senegalese nationals have been expelled from The Gambia into Senegal's Casamance region, BBC Afrique is reporting.
The measure comes only three days after a meeting held by the interior ministers of the two states in the Senegalese capital, Dakar.
Senegal played a key role in helping President Adama Barrow take power in January, forcing long-serving ruler Yahya Jammeh to go into exile.
The expulsions took place after undocumented Senegalese nationals were arrested by immigration authorities during spot checks in Banjul and its suburbs.
Last Wednesday, Gambian Interior Minister Mai Ahmad Fatty was in talks with his Senegalese counterpart Abdoulaye Daouda Diallo in a bid to work out a joint strategy to tackle cross-border crime, including drug trafficking and potential terror threats.
Gambia's immigration director, Buba Sanyang, ordered the expulsions without allowing those detained to appeal, BBC Afrique is reporting.
It quotes a Gambian government source as saying that the expulsions are not a reflection of President Barrow's immigration policy.
According to the source, no officials from the justice and interior ministries were consulted over the expulsions.
Before the expulsions, relations between Banjul and Dakar have been cordial. President Barrow was initially sworn in as president in Dakar, and Senegal sent troops to The Gambia to force Mr Jammeh out of power.
Mr Barrow defeated Mr Jammeh in elections, ending his 22-year rule.
However, Mr Jammeh tried to cling to power, alleging that the result was rigged.