UPDATE 2-TravelCenters of America says Arko's $1.4 bln bid not superior to BP

(Adds background on BP offer, TravelCenters' operations)

March 28 (Reuters) - TravelCenters of America on Tuesday confirmed Arko Corp's $1.4 billion takeover offer is not superior to its existing proposal from British energy giant BP Plc.

Store operator Arko said on Monday it had made a buyout offer for TravelCenters, which was higher than BP's $1.3 billion bid in mid-February.

But TravelCenters' board said Arko's proposal did not constitute a superior offer and had a high level of execution risk due to the latter's inability to secure committed financing.

The board also noted Arko's sub-investment grade credit rating was unattractive to Service Properties Trust, which owns most of TravelCenters' properties.

TravelCenters owns a network of about 281 highway sites across 44 U.S. states and offers services beyond fueling, including truck maintenance, restaurants, travel stores and parking, which account for 70% of the business's profit margin.

(Reporting by Arshreet Singh; Editing by Rashmi Aich and Krishna Chandra Eluri)