The assassination of Russian General Igor Kirillov in Moscow probably won’t impede peace talks, but was “not a good idea at all” for Kiev, US President-elect Donald Trump’s special envoy for Ukraine and Russia, Keith Kellogg, has said.

Kirillov, who commanded the Russian Radiological, Chemical, and Biological Defense Forces, was killed in an explosion in southeastern Moscow early on Tuesday. The Russian authorities have detained a suspect, whom they say was recruited by Ukrainian intelligence and paid to carry out the attack.

In an interview with Fox News on Wednesday, Kellogg was asked whether the murder of Kirillov would hinder peace talks between Moscow and Kiev, which Trump hopes to broker once inaugurated next month.

“I don’t think it’s really a setback,” he responded, “but I would say this: there are rules of warfare and there are certain things that you just kind of don’t do.”

“When you’re killing flag officers, general officers – admirals or generals – in their hometown, it’s kind of like you’re extending it and I don’t think it’s really smart to do it. It’s not kind of the rules of war,” he continued, reiterating that the bombing was “not a good idea at all, in my opinion.”

In light of the murder, former Russian President Dmitry Medvedev has warned that “all NATO decision-makers” from countries assisting Ukraine “can and should be considered legitimate military targets for the Russian state.”

Kellogg, formerly a lieutenant general in the US Army, confirmed to Fox News that he will travel to Kiev before next month’s inauguration on a “fact-finding” mission. Kellogg will not travel to Moscow, but according to a Bloomberg report earlier on Wednesday, he is open to the idea.

Previously a staunch supporter of increased military aid to Kiev, Kellogg was nominated as Trump’s special envoy for Ukraine and Russia last month. In an announcement on social media, the incoming president promised that Kellogg would help “secure PEACE THROUGH STRENGTH, and Make America, and the World, SAFE AGAIN!”

Back in June, Kellogg told Reuters that he had advised Trump to use military aid as leverage to force Moscow and Kiev into peace talks. “We tell the Ukrainians: ‘You’ve got to come to the table, and if you don’t come to the table, support from the United States will dry up,’” he told the news agency. “And you tell [Russian President Vladimir] Putin he’s got to come to the table and if you don’t come to the table, then we’ll give Ukrainians everything they need to kill you in the field.”

Trump has repeatedly promised to end the conflict within a day of taking office, without providing any detailed plan as to how he intends to achieve this goal.

Moscow maintains that any settlement must begin with Ukraine ceasing military operations and acknowledging the “territorial reality” that it will never regain control of the regions of Donetsk, Lugansk, Kherson, and Zaporozhye, as well as Crimea. In addition, the Kremlin insists that the goals of its military operation – which include Ukrainian neutrality, demilitarization, and denazification – will be achieved.