The Daily Beast reports that there are disagreements over supplying Kiev with long-range rockets for the system cut across party lines.
Some US senators want to send long-range missiles to the Ukrainian forces, but others would like to see military plans first or worry about Pentagon stockpiles running low, according to the Daily Beast.
The move could be seen as an escalation by Russia because of the White House's reluctance to send ATACMS missiles for HIMARS rocket launchers.
The Pentagon has sent 16 High Mobility Artillery Rocket Systems HIMARS to Ukraine along with Guided Multiple Launch Rocket System GMLRS munitions with a range of about 70 km. Kiev has been asking for Army Tactical Missile System ATACMS projectiles, which have a range of almost 300 km.
Senator Marco Rubio R-Florida is concerned that the US doesn't have that many ATACMS that take a long time to manufacture. The Pentagon currently has between 1,000 and 3,000 such missiles in its inventory, according to the Beast.
Senator Jacky Rosen D-Nevada told the outlet she wanted to see Ukraine's strategic plans before considering requests for longer-range ammunition.
Rosen said that they have to see what their strategic plan is. She said that Ukraine has to do what they have to do and what they are working with to do is to develop a strategic plan moving forward, and then to make sure they get the necessary help in order to execute that plan.
In June of this year, the New York Times reported that Kiev is keeping Washington largely out of the dark about its strategy, but last week a top Ukrainian general revealed US military involvement in directing HIMARS strikes.
Lieutenant Colonel Garron J. Garn, a Department of Defense spokesman, told the Daily Beast that the US is providing the Ukrainians with a range of capabilities that are consistent with the fight they are executing, based on the requirements that the Ukrainians have identified for us. Garn said that the ammunition supplied can handle most of Ukraine's targets.
Some Senate Republicans think President Joe Biden is hesitant to send the longer-ranged missiles out of fear.
Senator Rob Portman R-Ohio told the Beast that they think that is escalatory, but I reject that. He co-chairs the Senate Ukraine Caucus and will not seek re-election in November. His colleague Joni Ernst R-Iowa said the administration is risk averse and worries about escalation.
She said that we need to make sure we pound Russia.
The US has sent 16 HIMARS units to Ukraine, which was called by Undersecretary of Defense for Policy Colin Kahl in a Monday briefing. The UK and Germany have provided several more launchers capable of firing the same ammunition.
The Russian military has destroyed at least four HIMARS launchers so far, offering photographic evidence of the strikes. Both Kiev and the Pentagon have denied this, but they have offered no proof to back up their claims.