By Barbara Starr

The Pentagon plans to keep an aircraft carrier in the Mediterranean longer than planned as a military presence to reassure NATO allies following Russia’s intervention in Crimea, CNN has learned.

The Obama administration is expected to announce the development involving the USS George H. W. Bush on Thursday.

”It’s all in the vein of reassuring our NATO allies of our commitment to them,” one senior U.S. military official said. “This isn’t about flexing our muscle at the Russians.”

But several U.S. officials said the decision was part of a package of new military efforts to beef up the American presence.

One official said all U.S. military assets in the region are being looked at for “what stays, what goes, what gets moved around.”

Although the administration is focusing on diplomacy to resolve the Ukraine crisis, the military part of the equation was discussed in depth at a White House meeting on Tuesday, a military official said.

Asked about the decision regarding the USS George H.W. Bush, a senior administration official said don't expect a lot more muscle flexing or additional military steps between now and Sunday's referendum in which Crimeans will be asked whether they want to reunite with Russia or be part of Ukraine.

As for Secretary of State John Kerry's trip to London to meet with Russian Foreign Minister Sergey Lavrov, that official said they are seeing more of a willingness to engage in diplomacy on the part of the Russians. But the official cautioned they're not preparing for a huge diplomatic breakthrough.

Several officials confirmed that there are intensive discussions across national security agencies about a variety of military options to increase the U.S. presence in the region.

All of the officials, who are directly familiar with the discussions, say the issue of moving military assets presents a fundamental problem.

“We have to be seen as doing something, but are ships really going to change Putin’s mind?” a second official said.

For now, the U.S. assesses that Putin will continue to send small numbers of additional troops into Crimea, and is not looking to escalate the situation militarily.

The United States believes Russia has established a strong line of command and control into Crimea and “has set very tight rules of engagement” to keep the situation under control, the second official said.