Real estate mogul Sam Zell's Equity Residential (NYSE:EQR) has raised its minimum bid for a 26.5 percent stake in the long-running battle for control of Archstone, owner of more than 70,000 U.S. apartment units.

Earlier this week, the minimum bid was raised to $1.48 billion from $1.32 billion by Bank of America Corp. and Barclays Plc, which own the minority stake in the company. The banks also extended the deadline for Equity's option to buy the stake to April 19 from Feb. 19.

Buying a stake in Archstone would give Equity veto power over the company's decision making and create a potential path to full ownership, so such a deal represents a challenge to Archstone's majority owner, the estate of Lehman Brothers.

However, Lehman has the right of first refusal for the stake and can match Equity's price, thus blocking the deal. Lehman thwarted a similar offer from Equity last month, when Lehman matched Equity's $1.3 billion offer for a 26.5 percent stake in Archstone.

Equity is entitled to an $80 million breakup fee if Lehman matches the offer.

We are not shocked that EQR has shrewdly extended the timeline to keep its options alive, wrote Alexander Goldfarb, a REIT analyst with Sandler O'Neill + Partners L.P., in a Tuesday research note.

Goldfarb expects Equity to continue to push for control of Archstone, rather than settling for the breakup fee, but said Lehman is strongly committed to owning all of Archstone and would likely exercise its right of first refusal. If Equity was able to gain control of the 26.5 percent, the company could eventually carve out some assets or take over the entire company, although the chance of that was remote, wrote Goldfarb.

Either way, we believe the latest chess move speaks well of EQR's strategy, said Goldfarb, who maintained a Buy rating on the Equity's stock, which was trading at $57.50 on Tuesday afternoon.

Lehman and the real estate developer Tishman Speyer bought Archstone, then a publicly traded real estate investment trust, at the height of the boom for $22 billion in 2007. Bank of America and Barcalys would take over ownership following restructurings, but then sold half of their majority state to Lehman last month.

Equity's interest in the company is indicative of the strength of rental housing, which has enjoyed rent gains as vacancy rates tighten throughout the country.

Although Archstone's ownership remains in limbo, the company, which controls over 70,000 U.S. apartment units, remains aggressive when it comes to new acquisitions. On Tuesday, Archstone announced it bought a 131-unit apartment complex near Seattle for $47.5 million. In December, it bought a building in Manhattan for $131 million.