It is inappropriate for public officials to travel at the expense of private donors, State Comptroller Micha Lindenstrauss said on Wednesday, amid a public controversy concerning recent reports alleging Prime Minister Benjamin Netanyahu used private funds to pay for travel and dinners.

The State Comptroller's comments came after last week Israel's Channel 10 reported that the prime minister allegedly continued to accept private sponsorship for flights even after he returned to politics as a member of Knesset and finance minister in 2003.

In one instance described in the investigative report, Netanyahu travelled to an important conference at the American Enterprise Research Institute during his tenure as finance minister in 2004. The institute allegedly paid $23,000 dollars for Netanyahu and his wife's flights to the United States.

The prime minister's office issued a statement in response to the allegations, saying that the Channel 10 article "is part of an ongoing multi-year effort of [Channel 10 commentator] Raviv Drucker to besmirch the name of the prime minister and his family. No external body ever paid for Mr. Netanyahu's children's flights at any point when he was in public office."

Speaking following a meeting of the Knesset's State Control Committee, Lindenstrauss said Wednesday, in an apparent allusion to the "Bibi-tours" affair, that it was "inappropriate for public officials to travel at the expense of donors and philanthropists."

The State Comptroller is expected to hold a preliminary investigation of the findings of the Channel 10 report. One problem facing the probe is that many of the officials named in the Channel 10 expose did not fall under the jurisdiction of the State Comptroller's Office, which could create a difficulty in gathering evidence.

On Tuesday, Netanyahu filed a libel suit against Channel 10 over another report, according to which the premier failed to report all of his campaign donation as required by law.

Netanyahu's attorney David Shimron filed the first lawsuit against the Channel 10 News Company, journalist Raviv Drucker, editor Uri Rozen and the Nana 10 company - which alleges they were all party to publishing a false report using a document listing everyone who contributed and promised to contribute to Netanyahu's primary election campaign in 2005.

According to the suit, the report was published despite Netanyahu clearly stating prior to publication that its claims were without foundation.

Among other claims, the lawsuit argues that the report highlighted two donations made by the Falik family for $7,500 each - even though it was made clear to the channel before the report's broadcast that the $15,000 was returned to the family in December 2005.