The U.S. food group said on Wednesday it had a 1.52 percent take-up from Cadbury shareholders for the 10.5 billion pound ($16.8 billion) hostile bid by a first closing deadline of 1300 GMT (8 a.m. EST) on January 5.
It said the cash and shares bid, currently worth 767 pence per share, remained open until February 2, but analysts said Kraft would have to improve the terms to 800 pence or more to stand a chance of success.
Most investors will likely be waiting until a January 19 deadline for Kraft to raise its bid before deciding whether to accept.
Kraft will have to offer at least 810 pence to attract acceptances, said analyst Dirk Van Vlaanderen at Jefferies International.
Buffett's warning, which coincided with Swiss food group Nestle's
Buffett said on Tuesday his Berkshire Hathaway
MORE DEBT, LESS EQUITY
Analyst Martin Deboo at Investec Securities said Buffett's message was not to kill the deal but for Kraft to use more debt than shares to fund it, and he believes there is a 50:50 chance between Kraft winning with a bid of 820p and that of Cadbury escaping.
We read Berkshire not as trying to impose a veto, but challenging Kraft's management to back their convictions with more cash and less equity, Deboo said.
Cadbury shares closed off 0.9 percent at 772 pence.
Martin Dolan at Execution Research said Buffett's comment show the conflict between him and Kraft, and the latter will have to offer over 800p to encourage Cadbury to let Kraft see its books and says Kraft could pay an extra 60p per share.
Buffett's intervention and Nestle's decision has narrowed the premium of Cadbury's share price to the bid price to around 0.7 percent from nearly 10 percent on Monday.
Under Britain's takeover rules, Kraft has until January 19 to raise its bid while Cadbury shareholders have until 1300 GMT on February 2 to accept.
Potential bidders for Cadbury who have expressed an interest publicly, Hershey
Cadbury has until January 12 to come up with fresh information to defend itself against the Kraft bid when it is expected to pre-release its 2009 results, but has gained a three-day extension to January 15 to give some further financial details.
(Reporting by David Jones; Editing by Dan Lalor, John Stonestreet)
($1 = 0.6267 pound)