The troops reportedly entered The Gambia to ensure Adama Barrow assumes power as the country's new president.
According to a report by BBC, the troops entered The Gambia to ensure Adama Barrow assumes power as the country's new president.
The move was reportedly confirmed by a Senegalese army spokesman.
The move is coming shortly after the Nigerian Air Force confirmed flying over The Gambia in readiness to use military force on command.
Despite the international recognition accorded Barrow after he was sworn in, Jammeh has refused to quit with backing by the country's parliament.
West African leaders have threatened to remove Mr Jammeh by force - a move the UN Security Council backed their efforts.