Shares on the Athens Stock Exchange have opened sharply lower after Greece's new government renewed a pledge to seek bailout debt forgiveness despite growing pressure from European lenders to stick to austerity.

Amid wider European losses, Greek shares were down 4.2 percent in early trading Sunday, while borrowing rates were back up, pushing yields on the country's 3-year-bonds to more than 18 percent.

Prime Minister Alexis Tsipras in his inaugural speech in parliament late Sunday described an election pledge by his left wing Syriza party to seek debt restructuring as "irrevocable."

Tsipras argues Greece's debt will be increasingly unsustainable unless it receives generous repayment relief that would allow its battered economy to recover.