The cabinet has cleared the borrowing up to 2.5 billion US dollars from sovereign bonds to meet cashflows under this year's budget.
With US 10-year bonds yields falling in foreign markets, conditions in international markets were improving, Coomaraswamy said.
Sri Lanka is also planning to borrow about 2 billion US dollars separately under a debt management law.
The Treasury is expected to certify the 2018 debt number shortly which will allow Sri Lanka to borrow up to 10 percent of the debt for early repayment or other debt management.
Sri Lanka is expecting to borrow about 4.4 percent of debt, which may be about 480 billion rupees.
Deputy Governor S R Attygalle said the entire amount need not be borrowed in foreign currency.
Coomaraswamy said the central bank hoped to go to cabinet within the next two weeks to get approval for the second debt raising, which will be used to manage 2020 debt.
In 2020 there is a international sovereign bond maturing in October next year.
This year 65 percent of foreign debt has been repaid.
Coomaraswamy said the extra borrowing could be from sovereign bonds, syndicated loans, or Samurai bonds.
The World Bank has also indicated that it will provide a guarantee, which will help Sri Lanka cut interest costs, he said.