After weeks of tense negotiations, the House of Representatives approved on Saturday a massive $61 billion (57 billion euros) military and financial aid package for Ukraine, but the Washington-based think tank ISW warns that Ukrainian forces may suffer “additional setbacks” and will have to manage their dwindling weapons and ammunition until the new US support, which still has to be approved by the Senate and signed by President Joe Biden, arrives and is put to use.

These requirements and the logistics of moving the equipment from the US to the front lines “will likely mean that the new assistance will not begin to affect” the situation for Kyiv’s forces for weeks, the ISW said in its daily update on the war in Ukraine on Sunday.

“The situation on the front lines will therefore likely continue to deteriorate in the interim, particularly if Russian forces increase their offensive operations to take advantage of the limited window of opportunity before the new US aid arrives,” the report said.

However, the ISW also said that Ukraine will likely be able to blunt the current Russian offensive “assuming that resumed US assistance arrives in a timely manner,” and that “Ukrainian command may be more willing to take risks in the short term” knowing that more equipment is on the way.

In recent weeks, Ukraine has faced an intensified bombing campaign by Moscow’s forces targeting major cities and energy infrastructure, causing civilian casualties.

Kyiv’s authorities have been pleading for months for more weapons and ammunition to counter Russian air strikes and advances by its ground forces in the east of the country.

The Pentagon has said it would move quickly to get the aid to Ukraine if Congress approved it.

“We are prepared to execute a rapid assistance package,” likely to include “air defence and artillery capabilities,” Pentagon spokesman Pat Ryder said.

The ISW also noted that US officials have said they will be able to ship some munitions to Ukraine “almost immediately” from storage facilities in Europe, particularly much-needed 155mm artillery rounds and air defence missiles, but other types of aid will take weeks to arrive.

“Ukraine has steadily improved its military logistics over the past several months, but this new system has not yet accommodated a sudden large influx of materiel, nor would any system be able to immediately distribute large amounts of materiel across the entire front line,” the ISW warned.

As such, the report predicted that Kyiv’s troops will continue to face shortages of artillery ammunition and air defence interceptors in the coming weeks, allowing “Russian mechanised forces to make marginal tactical gains” and Moscow’s air force to “degrade Ukrainian defences” more severely if it seizes the opportunity to make more significant advances.

“ISW continues to assess that materiel shortages are forcing Ukraine to conserve munitions and prioritise limited resources to critical sectors of the front, increasing the risk of a Russian breakthrough in other, less well-supplied sectors and making the overall front line more fragile than the current, relatively slow rate of Russian advances suggests,” the think tank said.

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