The risk of Greece becoming insolvent is "increasing by the day," the head of the German central bank or Bundesbank, Jens Weidmann, said on Thursday.

"There is a strong determination to help Greece ... But time is running out, and the risk of insolvency is increasing by the day," Weidmann told a London investment seminar as Greece and its European partners intensify efforts for a bailout deal to prevent Athens from defaulting.