(Reuters) - French low-cost telecoms operator Iliad SA (ILD.PA) abandoned its attempt to buy T-Mobile US Inc (TMUS.N) on Monday because of resistance from majority owner Deutsche Telekom (DTEGn.DE), becoming the third bidder to walk away from the carrier in three years.

While Iliad's approach had been widely perceived as a long shot, its formal withdrawal sent shares of the U.S. carrier to a 10-month low. The move came three months after Sprint Corp (S.N) dropped its own bid to buy T-Mobile.

Now T-Mobile, which had been gaining market share thanks to aggressive marketing tactics, will face new questions about whether it can continue to prosper as an independent entity.

"There haven't been any other viable offers that have emerged since Sprint backed out, and that was not a formal offer to boot. There may be some questions about the price a larger buyer is prepared to pay in turn for a regulatory battle they may have to face," said Bill Menezes, an analyst at Gartner.

T-Mobile shares fell as much as 4.3 percent to $26.41, their lowest level since December 2013. The stock ended 2.5 percent lower at $26.92.

A person familiar with Deutsche Telekom's thinking said on Monday that the group preferred to keep its U.S. business longer since it was unconvinced that Iliad, as a newcomer to the U.S. market, could run the business better than its current management.

T-Mobile US and Deutsche Telekom, which owns 66 percent of the business, declined to comment. Iliad said it would now "continue its profitable growth policy as it has been conducted over the last 15 years."

Iliad had set a mid-October deadline to decide whether to improve its $33 a share bid for 56.6 percent of the fourth-biggest cellphone network operator in the United States, sources told Reuters last month.

The low-cost telecoms operator set up by maverick French tycoon Xavier Niel said it had formed a consortium with two "leading private equity funds" to bid for 67 percent of T-Mobile US at $36 per share including cost savings. Excluding the synergies, the bid was for $33 in cash per share, the same level as Iliad's original offer in late July for 56.6 percent of the company, said a person familiar with the situation.

Deutsche Telekom believes it is better off waiting to see if deals with the likes of Sprint or satellite TV provider Dish Network Corp (DISH.O) become possible under a different U.S. administration with a more favorable view on consolidation, the person said.

Another person close to Deutsche Telekom's management said the new offer was not a significant improvement. "It would not have made any sense to leave Deutsche Telekom with still a large stake of equity exposed to a company they have serious doubts about," the person said.

Deutsche Telekom, which makes about a third of its sales and a fifth of core profit in the United States, has tried to sell T-Mobile twice since late 2011 because it sees it as too small to compete with market leaders Verizon Communications Inc (VZ.N) and AT&T Inc (T.N).

Regulators rejected AT&T's $39 billion bid for T-Mobile US three years ago.

T-Mobile has been searching for a buyer with access to U.S. spectrum licenses and an American customer base, Jefferies analyst Mike McCormack said in an analyst note after meeting with T-Mobile's investor relations team last month.

The note has fueled rumors that Dish, which has been stockpiling billions of dollars' worth of wireless spectrum, may be a potential suitor for the company.

In August, Dish Chairman Charlie Ergen said it makes sense for the company to consider making a bid for T-Mobile now that Sprint is out of the picture.