China and the Vatican will establish formal diplomatic relations sooner or later because Pope Francis has the "wisdom" to resolve problems between the two sides, a state-run Chinese newspaper said Tuesday, amid increasing controversy over the issue.

A framework accord between the Vatican and China on the appointment of bishops is ready and could be signed in a few months in what would be an historic breakthrough in relations, a senior Vatican source said last week.

But on Monday, Cardinal Joseph Zen, 86, the outspoken former bishop of Hong Kong said the Vatican is selling out China's underground Catholics and "forcing them into a bird cage," raising the ante in his recent criticisms that had already sparked a rebuke from the Vatican.