President Mahinda Rajapakse, whose ruling United People's Freedom Alliance took victory in this month's parliamentary election, will bring in five more cabinet ministers and one deputy minister soon, the official said.
His cabinet, sworn in Friday, currently numbers 37 excluding the president himself, who holds the defence, finance, ports and highways portfolios.
Rajapakse was re-elected for a second term in presidential polls in January and cemented his grip on power when his ruling coalition won 144 seats in the 225-member parliament two weeks ago.
"There will be three more ministers from the (central) Kandy district and two more from elsewhere," the source said, declining to be named.
The five had not been named to the cabinet in Friday's announcement due to "technicalities" and would be sworn in within a few days, he said.
The cabinet is far smaller than the record 109 ministers and deputy ministers in the last government, which had been lambasted as cumbersome and wasteful.