The South African rand firmed early on Tuesday, ahead of the release of a key economic indicator by the country's central bank.

At 0636 GMT the rand traded at 18.70 against the dollar, roughly 0.3% stronger than its previous close on Monday.

The central bank will publish its composite leading business cycle indicator around 0700 GMT, providing data that includes vehicle sales, business confidence and money supply in Africa's most industrialised nation.

The risk-sensitive rand has endured bouts of volatility, hurt by political disputes between the two biggest parties in the coalition government - the African National Congress and the Democratic Alliance (DA) - over a proposed increase to value-added tax on May 1.

The DA and other smaller parties have publicly rejected the proposal and filed a court case challenging the legality of the budget process. The case will be heard at on Tuesday.

South Africa's benchmark 2030 government bond was weaker in early deals, with the yield up 4.5 basis points at 9.215%.