US president Joe Biden dropped his opposition to Ukraine firing US missiles at targets deep inside Russia in response to North Korea's entry to the war, a shift in US policy that took on added urgency following Donald Trump's November 5th election win, sources familiar with the matter said.
Mr Biden for months resisted pleas from Ukrainian president Volodymyr Zelenskiy to ease limits on the use of US-supplied ATACMs missiles, which can reach far into Russian territory, wary of potentially drawing Nato into a conflict with a nuclear-armed power.
But Moscow's decision to deploy North Korean soldiers to Russia's Kursk region represented a major escalation that demanded a response, a senior US official and two other sources familiar with the matter told Reuters.
The election of Mr Trump - who is deeply sceptical of US support for Ukraine - added pressure on the administration to loosen the rules on the use of the weapons and take other steps to bolster Ukraine as it suffers repeated setbacks on the battlefield, said two other sources familiar with the matter.
The decision could help to "Trump-proof" parts of Mr Biden's Ukraine agenda by strengthening Ukraine's position in case they lose US support, one of the sources said.
Mr Trump has repeatedly criticised US military aid to Ukraine, raising fears that he might suspend weapons supplies.
The relaxation of the restrictions on US weapons may have come too late to alter the course of the conflict but could help Ukraine defend the foothold it has in Kursk.
The White House did not immediately respond to a request for comment.
A State Department spokesperson declined to say whether Mr Biden had authorised the longer-range strikes but said Russia was escalating the conflict by deploying North Korean troops.
Moscow has vowed to respond to what it sees as an escalation by the West. A US official said on Thursday that Russia may have fired an intermediate-range ballistic missile during an attack on the Ukrainian city of Dnipro, in a likely warning to Nato.
Strengthening Kyiv's hand
The relaxation of US conditions was conveyed to Ukraine during a November 12th call between secretary of defence Lloyd J Austin and Ukrainian minister of defence Rustem Umerov, said a source familiar with the discussions.
A day later, secretary of state Antony Blinken informed Nato secretary-general Mark Rutte and European officials of the decision as well as his Ukrainian counterpart, Andrii Sybiha, during a trip to Brussels, a senior US official said.
Ukraine conducted its first long-range strike under the new policy on Tuesday, announcing it had fired US ATACMS missiles on an arms depot about 110 km inside Russia.
British missiles
Mr Biden's easing of weapons restrictions appeared to open the door for US allies to allow their own weapons to be used in new ways. On Wednesday, Ukraine fired a volley of British Storm Shadow cruise missiles into Russia.
Since the elections, the Biden administration has taken other actions to support Kyiv, approving the use of anti-personnel mines to slow Russia's advance in Ukraine's east and allowing US defence contractors to work inside Ukraine to repair US-supplied weapons, enabling the Ukrainians to keep more of the gear in active use.
For months, Ukrainian officials pleaded with Americans to let them use the 190-mile range rockets for targets deeper inside Russian territory, arguing that their inability to hit air bases hosting warplanes involved in strikes on Ukraine was a major handicap.
But the Biden administration declined to give a green light.
US officials have been sceptical of the value of letting Ukraine use weapons such as the ATACMs, arguing that Moscow has already moved some bombing targets out of range, and that Ukraine already has domestically made rockets and kamikaze drones that can reach into Russian territory.
They have also worried that such a move could risk a direct war between Nato and Russia, a possibility some experts and US lawmakers have downplayed.
North Korean troops
Russia's decision to deploy thousands of North Korean troops to join the fighting changed the administration's thinking.
The US acknowledged in late October that it had seen evidence of North Korean troops in Russia for possible deployment in the Ukraine conflict.
North Korean soldiers had docked in the eastern port city of Vladivostok, after boarding ships in early-to-mid October from North Korea's Wonsan region, and were taken to three military training sites in eastern Russia, White House spokesperson John Kirby told reporters.
The following week Mr Blinken said as many as 8,000 North Korean forces were in Kursk, where Ukrainian forces have controlled territory since August.
Easing US controls on the use of the missiles was intended to send a message to the North Koreans and Russians that the shift was unacceptable, as well as hamper their efforts to push Ukrainians out of Kursk, said a senior US official familiar with the administration's thinking.
The official acknowledged that relaxing the restrictions risked a further escalation of the conflict - but noted that Russia has so far taken no action against states other than Ukraine.
And a congressional aide said they believed the new policy only applied to the Kursk region.
"Ukraine is only authorised to shoot deeper into Russia to constrain the Russian-North Korean effort to push Ukraine out of the Russian territory," the aide said.
