LONDON, March 7 (Reuters) - Belgian insurer Ageas has brought in an additional adviser as it presses ahead with a potential takeover offer for Britain's Direct Line , three sources familiar with the matter told Reuters.

Ageas has lined up Deutsche Bank to work alongside its existing financial adviser Bank of America , two of the sources said. It interviewed banks for additional support since making its offer public last week, the third one added.

Ageas might sweeten the terms of its initial bid to win over Direct Line's leadership, two of the sources said.

Ageas declined to comment, and has until March 27 to launch a formal offer or walk away under UK takeover rules. Deutsche Bank and Direct Line declined to comment.

Direct line shares traded up as much as 4% on the day to 225 pence after the Reuters story, and were last up 2.3% at 221.3 pence.

Direct Line last week rejected Ageas' 3.1 billion pound ($3.95 billion) cash-and-stock proposal as it believed it undervalued the company.

It has also boosted its advisory line-up by bringing in boutique Robey Warshaw, another person familiar with the move said. Robey Warshaw declined comment.

The four sources spoke on condition of anonymity because the efforts are private.

Direct Line shares have risen around 32% since Ageas' offer became public. The offer would give its shareholders a 22% stake in the combined group. Shares in the British home and motor insurer had closed at 216.3 pence on Wednesday, below the 233 pence per share proposed by Ageas.

($1 = 0.7842 pounds) (Reporting by Pablo Mayo Cerqueiro and Amy-Jo Crowley. Additional reporting by Andres Gonzalez; Editing by Anousha Sakoui, Barbara Lewis and Chizu Nomiyama)