WASHINGTON (AP) — The U.S. on Wednesday unveiled a new $700 million package of sophisticated weapons for Ukraine in an urgent effort to prevent Russia from seizing the final swaths of land in the Donbas region. But the most advanced rocket systems will take at least three weeks to reach the battlefront, raising questions of whether they will arrive in time to stop Russia’s slow but steady gains.

The Biden administration’s decision to send four medium-range rocket systems came after weeks of debate over whether the precision-guided weapons would provoke a strong military reaction from Russian President Vladimir Putin. It suggested the U.S. believes it has zeroed in on what weapons deliveries are worth the risk.

“We don’t have an interest in the conflict in Ukraine widening to a broader conflict or evolving into World War Three. So we’ve been mindful of that,” said Colin Kahl, the defense undersecretary for policy. “But at the same time, Russia doesn’t get a veto over what we send to the Ukrainians.”

Still, Kahl and other U.S. officials said that Ukrainian leaders have promised they will use the rockets only to defend their nation.

“The Ukrainians have given us assurances that they will not use these systems against targets on Russian territory,” Secretary of State Antony Blinken said Wednesday. “There is a strong trust bond between Ukraine and the United States.”

However, Kremlin spokesman Dmitry Peskov told reporters Wednesday the U.S. is “deliberately and diligently pouring fuel on the fire.” He added that Russia doesn’t trust Kyiv’s assurances that the multiple rocket launch systems supplied by the U.S. will not be used to attack.

“In order to trust (someone), you need to have experience with situations when such promises were kept. Regretfully, there is no such experience whatsoever,” Peskov said.

The need to train Ukrainian troops on the HIMARS system for about three weeks before they can go to battle raises concerns that Russia will have a window of time to capture key terrain in the east.

“It is a grinding fight,” said Kahl. “We believe that these additional capabilities will arrive in a timeframe that’s relevant and allow the Ukrainians to very precisely target the types of things they need for the current fight.”

The Pentagon would not say how many rockets it will provide to Ukraine, only that it is sending four of the truck-mounted HIMARS systems. The trucks each carry a container with six precision-guided rockets, which can travel about 45 miles (70 kilometers).

The expectation is that Ukraine can use the rockets in the Donbas, where they could both intercept Russian artillery and take out Russian positions in towns where fighting is intense, such as Sievierodonetsk.

Sievierodonetsk is important to Russian efforts to capture the Donbas before more Western arms arrive to bolster Ukraine’s defense. The city, which is 90 miles (145 kilometers) south of the Russian border, is in an area that is the last pocket under Ukrainian government control in the Luhansk region of the Donbas.

President Joe Biden in an essay in a New York Times, said that, “We are not encouraging or enabling Ukraine to strike beyond its borders. We do not want to prolong the war just to inflict pain on Russia.”

The package announced Wednesday is the 11th approved so far and will be the first to tap the $40 billion in security and economic assistance recently passed by Congress. It includes a variety of weapons and equipment, ranging from helicopters, Javelin anti-tank weapon systems and radars to tactical vehicles, artillery rounds and spare parts.

The weapons will come from Pentagon drawdown authority, so would involve taking them from U.S. inventory. Kahl said that the HIMARS systems have already been sent to Europe, and officials said the training could begin this week.

Since the war began in February, the U.S. and its allies have tried to walk a narrow line: Send Ukraine weapons needed to fight off Russia but stop short of providing aid that will trigger a broader conflict that could spill into other parts of Europe.

Over time, however, the U.S. and allies have amped up the weaponry going to Ukraine, as the fight has shifted from Russia’s campaign to take the capital, Kyiv, and other areas, to more close-contact skirmishes for small pieces of land in the east and south.

To that end, Ukrainian President Volodymyr Zelenskyy has been pleading with the West to send multiple-launch rocket systems as soon as possible to help stop Russia’s destruction of towns in the Donbas. The rockets have a longer range than the howitzer artillery systems that the U.S. has provided Ukraine. They would allow Ukrainian forces to strike Russian troops from a distance outside the range of Russia’s artillery systems.

“We are fighting for Ukraine to be provided with all the weapons needed to change the nature of the fighting and start moving faster and more confidently toward the expulsion of the occupiers,” Zelenskyy said in a recent address.

Ukraine needs multiple-launch rocket systems, said Philip Breedlove, a retired U.S. Air Force general who was NATO’s top commander from 2013 to 2016.

“These are very important capabilities that we have not gotten them yet. And they not only need them, but they have been very vociferous in explaining they want them,” said Breedlove. “We need to get serious about supplying this army so that it can do what the world is asking it to do: fight a world superpower alone on the battlefield.”

Russia has been making incremental progress in the Donbas, as it tries to take the remaining sections of the region not already controlled by Russian-backed separatists.

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AP Diplomatic Writer Matthew Lee, AP writer Aamer Madhani and AP broadcast reporter Sagar Meghani contributed to this report.

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