The U.S. Treasury's decision to increase buybacks of long-term debt has temporarily brought yields down from elevated levels, but the impact could prove short-lived as it fails to address concerns about high levels of debt and government spending, analysts said.

In an unexpected move, the Treasury on Wednesday said that it would double the size of its buyback operation of long-dated Treasurys to at least $4 billion from $2 billion per operation, targeting nominal coupon securities with maturities of 10 years or longer.

The Treasury said the increase in buybacks reflects its desire to provide greater liquidity in longer-dated nominal securities.

"Beyond the increased flexibility to manage market liquidity, we view this announcement primarily as a signal that U.S. policymakers might well get creative in addressing the worryingly high refinancing costs at the long end of the [Treasury] curve," Metzler's analysts said in a note.

The policy shift directly targets the recent surge in U.S. Treasury yields, which pushed the 30-year yield to a 19-year high of 5.337% on Tuesday, according to Tradeweb. Long-end U.S. Treasury yields fell following the decision on Wednesday and continued to do so in Asian and early European trade on Thursday.

However, the decline showed signs of fizzling out.

The 10-year Treasury yield last rose 1.9 basis points to 4.671%, while the 30-year yield was up 3 basis points at 5.223%, according to Tradeweb.

The unexpected buyback announcement is a sign "of increasing administration unease on the ongoing rise in long-end U.S. yields," George Saravelos, global head of FX research at Deutsche Bank, said in a note.

Market watchers voiced concerns that the measure in itself won't be sufficient to tame the rise in yields over the long term.

Without a credible plan to keep debt in check, investors will demand a higher term premium, or greater compensation for buying longer-term debt, said Erik Liem, rates strategist at Commerzbank, in a note.

"While long-end off-the-run Treasurys will benefit directly from the flow-effect, the longer-term implications are less clear-cut," he said.

Low investor conviction could leave long-dated Treasury yields under sustained pressure, TD Securities' rates strategists Gennadiy Goldberg and Molly Brooks said in a note.

In order for pressure on long-end Treasurys to abate, the market needs some combination of the Federal Reserve "sounding more credible on inflation," the Treasury hinting more strongly at decreasing long-end supply, investor demand improving, corporate-bond supply moderating, or growth concerns resurfacing, they said.

Greater issuance of shorter-term debt leads to its own problems, with a risk of greater volatility as debt needs to be replaced more frequently.

"As buybacks need to be funded with cash or bills, they lead to a reduction in the weighted average maturity of debt, which increases interest rate and rollover risks," Commerzbank's Liem said.

The Federal Reserve's minutes of the July meeting, also released on Wednesday, received less attention amid the buyback announcement, but revealed growing concerns about elevated levels of inflation.

The DXY dollar index, which measures the currency's value against a basket of currencies, fell to a three-month low of 98.669 in early European trade.

The Treasury's buyback plan risks proving counterproductive if investors remain concerned about U.S. fiscal risks, potentially leading to reduced appetite for holding U.S. assets or the dollar, MUFG analysts Derek Halpenny and Abdul-Ahad Lockhart said in a note.

"Even if the Treasury buyback plan does contain yields, the U.S. dollar now remains more vulnerable to the downside on the fact that yields are potentially lower," they said.