While placing those latter two ratings on CreditWatch, S&P added that it saw a one-in-two chance Venezuela night default again within the coming three months.
Venezuela's state-run oil company PDVSA has also been declared in default by rating agencies Fitch and Moody's.
Venezuela faced the first of what could be a cascade of defaults on its $150-billion foreign debt Tuesday as Standard and Poor's declared the crisis-torn South American country in "selective default".
Venezuela's total external debt, which also includes loans from countries like Russian Federation and China, is thought to be as much as $140bn.
Though it has teetered on the brink for years, Venezuela recently failed to make $200 million in coupon payments on bonds worth $5 billion owed to foreign creditors, according to S&P.
On Monday, government officials met with creditors in Caracas in an attempt to restructure its debt.
Vice-president El Aissami blamed USA sanctions for delays to Venezuela's debt repayments.
Participants in the creditors' meeting said at least one attendee left the room when it became clear Mr Aissami would be leading it.
The sanctions also impose a ban on U.S. entities buying any new Venezuelan debt issues, complicating the government's debt restructuring plan.
"We rate this meeting, in which Venezuelan debt holders from Venezuela, the United States, Panama, the United Kingdom, Portugal, Colombia, Chile, Argentina, Japan and Germany participated, as highly positive and very auspicious", the statement continued. The government held a meeting with bondholders in Caracas on November 13 about a debt restructuring (generally considered akin to default), which is typically used to determine how much less investors will be paid than officially owed.