In an interview broadcast Monday, Bill Clinton, the US leader from 1993 to 2001, defended donations to his foundation that raise questions about influence peddling as his wife, former Secretary of State Hillary Clinton, runs for the Democratic presidential nomination. The former president's Clinton Foundation has regularly accepted money from foreign sources.

"I gotta pay our bills," Clinton told NBC News from Kenya when asked about his speeches - for which he sometimes charges more than $500,000 (450,000 euros) - in an interview taped over the weekend to air late Monday. "We do our best to vet them. And I have turned down a lot of them."

Tuesday will see publication of "Clinton Cash," a book covering potential conflicts involving the former president's foundation, which has accepted foreign funding for its endowment and for its charitable work abroad.

Chorus of critics

State Department officials do not believe that donations influenced Clinton when she served as the top US diplomat. On Monday, spokesman Jeff Rathke said department officials had heard reports suggesting links between the secretary of state's work and donations from foreign governments. However, Rathke said that during Clinton's tenure as secretary of state, the department received requests to review proposed speech hosts and consulting deals for her husband and found no conflicts.

Clinton's lawyer sent a letter to a congressional panel investigating the 2012 attack on the US consulate in Benghazi, Libya, offering for the former secretary of state to testify on Capitol Hill this month. She had previously addressed the panel in January 2013, while she was still the secretary of state.

Earlier this year, Clinton admitted that while serving as secretary of state she had communicated through a private email account, with messages stored off government servers. South Carolina Republican Representative Trey Gowdy, the chairman of the House panel, had requested that Clinton face the body at least twice - once to talk about her email account.

The embattled but, many say, inevitable Democratic candidate is no longer the only woman running. Former Hewlett-Packard CEO Carly Fiorina, a failed California senatorial candidate in 2010, officially entered the race Monday on the nationwide television show "Good Morning America" and Twitter.

Clinton's only opponent for the Democratic nomination so far is the independent Vermont Senator Bernie Sanders.

mkg/kms (Reuters, AFP, dpa, AP)