Some European countries that have sent weapons to Kiev are running out of stockpiles, and defense contractors may take years to make up the shortfall, Bloomberg writes.

According to sources, NATO countries are urging defense companies to increase production to help them replenish supplies - both to replenish stocks in Ukraine and to bolster their own amid heightened tensions.

Kyiv's allies have already sent billions of dollars worth of weapons, ammunition and equipment. This is putting pressure on ammunition stocks, including 155mm artillery shells. The U.S. has provided more than a million shells to Ukraine since the war began.

Defense companies in the U.S. and Europe are now seeing increased demand for air defense systems and anti-tank weapons along with other equipment, and governments are increasingly recognizing that Ukraine is likely to need military support in the coming years.

But rapidly expanding production after decades of limited orders will not be easy. As the war drags on, Ukraine's partners may be tempted to reduce support as they worry about their security needs, potentially leading to friction.

In addition to multiple rocket launchers, Ukraine's allies have largely focused on sending it Soviet-era weapons and tanks, which are also running out of stock. These stocks need to be replaced with modern weapons

At the same time, North Atlantic Treaty Organization members need more weapons to strengthen the alliance's presence on its eastern flank. Defense ministers will meet this week in Brussels to discuss these issues, following a meeting of national weapons directors in late September.

It could be years before supply equals demand. Defense companies face obstacles to expanding production to the scale needed. European defense firms will also have to modify assembly lines after many governments cut defense spending after the Cold War.