Venezuela signed a debt restructuring deal with major creditor Russia on Wednesday, a diplomatic source told AFP, as ratings agencies declared Caracas in partial default. 

The country is seeking to restructure its foreign debts, estimated at around $150 billion, after it was hit hard by tumbling oil prices and American sanctions. 

The source did not give  details of the deal, which are set to be made public at a press conference at the Venezuelan embassy attended by the country's finance minister Simon Zerpa. 

S&P Global Ratings meanwhile said it had placed Venezuela's state-owned oil company PDVSA in "selective default" after it failed to make its interest payments on some of its debt. 

The ratings agency this week declared the country itself in selective default after it failed to make $200 million in payments on two global bond issues. 

Fitch also downgraded PDVSA and cash-strapped Venezuela over delayed payments, but Caracas insisted it was in the process of paying up.