KYIV, Dec 19 – U.S. intelligence community estimates there may be four weeks available to diffuse a potential crisis as Russia is preparing a new attack on Ukraine, CNN reported Sunday citing a senior U.S. official.

U.S. President Joe Biden directed his national security team to use every tool possible to try to deter Russian President Vladimir Putin while a possible invasion was still assessed to be several months away, a senior US official told CNN.

"What we have been doing is very calculated," the official said. "But we only have about a four-week window from now" to pull it off, he added.

The response began with a flurry of intense diplomatic activity in early fall, including a trip by CIA Director Bill Burns to Moscow to warn Putin directly against making a move.

But as Russian troops continued to amass near Ukraine's border, the quiet diplomacy quickly evolved into stark, public warnings to Putin to back down or face harsh sanctions and increased US military assistance to Ukraine. Top Biden officials are now emphasizing that the consequences would go above and beyond anything Russia faced after its land grab in 2014.

"The sanctions we imposed on Russia in 2014 were largely intended to inhibit the medium-to-long-term development of specific Russian state-owned firms by restricting their access to US capital markets and technology," a White House official said.

In contrast, the options on the table now "would be overwhelming, immediate and inflict significant costs on the Russian economy and their financial system."

The intelligence community came under fire in 2014 when Biden was vice president, over what some lawmakers said was a failure to predict Russia's incursion into Crimea until it was too late. And after that attack, Biden's push to arm Ukraine and impose extremely severe sanctions on Russia was largely overruled by President Barack Obama.

Still, current and former officials told CNN they see some similar mistakes being made -- and similar signs from Russia that it is not taking the US threats seriously.

"I am definitely seeing things that are being done better in terms of them taking the threat seriously and working very closely with our allies, which I think is essential," said Lt. Gen. Ben Hodges, who served as commanding general of United States Army Europe from November 2014 to December 2017.

“But there are still a lot of mixed messages coming out of the White House and a couple of unforced errors that the Kremlin must be quite happy with," Hodges said, including Biden's disclosure earlier this month that sending US troops to Ukraine is not on the table.

"I agree this is not the time for US military action," he said. "But why announce that? That was basically a concession while the Kremlin has only increased their demands." (cnn/ez)