Atlas Arteria (ASX:ALX) said IFM Global Infrastructure Fund subsidiary Diamond Infraco 1 has increased its takeover offer to AU$5.10 per security from AU$4.75 and declared it "best and final," according to a Monday filing with the Australian bourse.

The revised offer represents a nearly 18% premium to the company's closing price on April 24.

The bidder said it will not raise its offer unless a rival bid emerges and has committed not to buy securities above AU$5.10 for 12 months after close unless a competing offer arises, per the filing.

The offer has been declared unconditional, subject only to specified prescribed occurrence conditions, with the bidder holding a 34.59% voting interest in the company, the filing said.

The offer remains valid until June 25, unless extended, the filing added.