The Pentagon's watchdog is establishing a new team in Ukraine to monitor ongoing US security assistance to Kyiv as a growing number of Republicans call for more oversight into how the money is being used.

The Defense Department inspector general said a senior representative from the US began work in Ukraine in late-August, and additional personnel are expected to arrive by the end of September. The positions are based at the US embassy in Kyiv to monitor US aid, which has totaled more than $43.7 billion since the start of the Biden administration.

It marks the first time the DoD IG will have personnel based in Ukraine since Russia's invasion in February 2022, said spokeswoman Megan Reed.

The establishment of the new team comes at a critical time for Ukraine aid. The Biden administration recently asked Congress for $24 billion more in assistance to Kyiv, including $13 billion in security assistance, as the president and other senior administration officials have vowed to continue US aid for "as long as it takes."

But an increasingly skeptical Republican Party has raised questions about how much bipartisan support there is for such substantial sums of aid to continue. A growing number of Republicans have begun questioning the wisdom of spending billions of dollars in Ukraine and have called for greater oversight.

House Speaker Kevin McCarthy has said he does not support a "blank check" to Ukraine, while the Republican-led House Oversight and Accountability committee vowed in February to make sure government agencies were monitoring the funds transferred to Kyiv "to prevent and reduce the risk of waste, fraud, and abuse." House Republicans have called for a special inspector general for Ukraine assistance, similar to SIGAR -- the Special Inspector General for Afghanistan Reconstruction -- which issued scathing criticisms of US waste in Afghanistan during the United States' longest war.

But, Republican calls for more oversight are not unanimous. Republican Senate leader Mitch McConnell said Tuesday that there was already "unprecedented insight into how nearly 30 types of Western weapons systems and vehicles are being used by Ukraine, often down to the serial number."

The Pentagon has improved its ability to monitor transfers of weapons and equipment to Ukraine through the defense attache in Kyiv and the establishment of the Security Assistance Group-Ukraine, but the military struggled to effectively oversee the shipments when the war began.

A Defense Department inspector general report obtained by CNN warned that the ability of the US to monitor billions of dollars in aid flowing into Ukraine faced "challenges" because of the limited US presence in the country. During the first six months of the war, the Office of Defense Cooperation-Kyiv "was unable to conduct required [end-use monitoring]" of military equipment provided to Ukraine.

The report, dated October 2022, underscored how difficult it was for the US to track the vast quantities of weapons, ammunition and equipment that went to Ukraine during the early months of the war. Criminals, volunteer fighters and arms traffickers in Ukraine attempted to steal some of the Western-provided weapons and equipment before it was recovered by Ukrainian intelligence, the report found.