* Accumulation of debt "unsustainable" - Treasury
* Treasury plans up to $1.5 bln bond this financial year
* Wants to issue more Sukuks to boost liquidity (Adds bond, Sukuk plans, quotes)
By Wendell Roelf
CAPE TOWN, Oct 13 (Reuters) - South Africa's weak economic growth, public-sector wages and financial support for state-owned companies that exceeds their budgets are the three main threats to the country's fiscal outlook, the National Treasury said on Tuesday.
Increased debt while growth is slow would only add to debt-service costs and increase the risk that South Africa's credit rating would be cut below investment grade, the Treasury said in a report to parliament's standing committee on finance that was made public on Tuesday.
"Accumulation of debt in the context of a low-growth environment is unsustainable," the Treasury said, noting that South Africa's debt-service costs are already its fastest growing expenditure.
South Africa had planned to issue $1 billion to $1.5 billion in a bond denominated in a foreign currency by the end of the financial year, although it has enough deposits to service its debt without new funds, the Treasury said.
"We don't have pressure necessarily to issue at a specific time. We also have foreign currency deposits that are enough for us to meet our commitments without necessarily raising money," Director-General of the Treasury Lungisa Fuzile told reporters.
South Africa would also like to issue more Sukuk bonds from "time to time" in order to increase liquidity.
"What we want to do is to do enough issues of the Sukuk that there is, if you will, a Sukuk curve that exists for South Africa," he said.
In August, Finance Minister Nhlanhla Nene said the government was concerned that an economic downturn would make it harder to raise revenue and that it would have to look at spending curbs.
Africa's most developed economy expects a budget deficit of 3.9 percent of GDP for the 2015/2016 financial year, but it wants to limit borrowing, partly to appease ratings agencies, which have downgraded such emerging markets as Brazil. (Writing by Stella Mapenzauswa and Joe Brock; Editing by James Macharia, Larry King)