Venezuela failed to make repayments totalling $237 million on two loans, which have overrun their 30-day grace period, ratings agency S&P announced Wednesday.
The oil-rich, cash-poor South American country failed to make the payments on bonds due 2025 and 2026, S&P said in a statement.
The ratings agency also warned of a "one-in-two chance that Venezuela could default again within the next three months."
"Two additional coupon payments are overdue, but within their grace period. We could lower the ratings on the following issues to 'D' if the government fails to pay within the stated grace period," it said.
Global ratings agencies had already declared Venezuela and state-owned oil company PDVSA to be in "selective default" due to the late payments on multiple bond issues.
Struggling under an estimated debt burden of $150 billion, Venezuela's President Nicolas Maduro said earlier this month that he wants to restructure Venezuela's sovereign debt as well as that of PDVSA.
PDVSA is the primary source of income for Venezuela, a country that sits atop the world's biggest oil reserves.
S&P said it would "very likely" consider any Venezuelan restructuring equivalent to a default.
"In addition, in our opinion, US sanctions on Venezuela and government members will most likely result in a long and difficult negotiation with bondholders," it said.
The sanctions from Washington, which has labeled the Maduro regime a dictatorship, prohibit US individuals and banks from buying new Venezuelan bonds, a requirement for any debt resolution.
Caracas has only $9.7 billion in foreign reserves and needs to pay back at least $1.47 billion in interest on various bonds by the end of the year, and then about $8 billion in 2018.