WASHINGTON (AP) — Hewing to a hard line, President Barack Obama warned congressional Republicans on Wednesday not to inject the threat of a government default into complex fiscal cliff negotiations aimed at avoiding year-end tax increases and spending cuts that could harm the economy.

"It's not a game I will play," declared Obama as Republicans struggled to find their footing in talks with a recently re-elected president and unified congressional Democrats.

Among the Republicans, Sen. Tom Coburn of Oklahoma became the latest to break ranks and say he could support Obama's demand for an increase in tax rates at upper incomes as part of a comprehensive plan to cut federal deficits.