MOSCOW/Donetsk, Ukraine (Reuters) - In the fall of 2015, pro-Russian separatists in Ukraine were introduced to a moustachioed new commander who, like his predecessors, went by the codename Tuman - "fog" in Russian.

Valery Asapov, right, poses for a photo with Russian President Vladimir Putin, during an award ceremony in the Kremlin in Moscow, Russia, February 22, 2013. Associated Press

Also like his predecessors, he appeared to be a Russian national. He signed documents as General Primakov.

When he was killed while on official assignment to Syria two years later, it turns out that this name was also fake, a deception to hide Russia's central role in a conflict that Moscow and the rebels maintain was entirely homegrown.

In fact, Valery Asapov was a Russian general working undercover.

The Kremlin has repeatedly denied providing military support for separatists who rejected a new pro-Western leadership in Kiev in 2014 and set up two states in eastern Ukraine, where many people identify as ethnically Russian. People pay their respects next to the coffin containing the body of Russian Lieutenant-General Valery Asapov who was killed by Islamic State shelling near Deir al-Zor, during his funeral ceremony at a military cemetery outside Moscow, Russia September 27, 2017. Reuters

Five rebels independently told Reuters that Asapov was a commander in the armed forces in one of them, the self-proclaimed Donetsk People's Republic.

Specifically, two of the rebels said, Asapov commanded the rebels' key armed division, the First Army Corps.

Asapov's younger brother Vyacheslav also confirmed that his brother was in Ukraine.

"He was there. For an entire year," he told Reuters in September, several days after giving a eulogy at his brother's funeral.

"How did he feel about it? He was okay with it, like any military man," he said by telephone from the Asapovs' hometown in the Kirov region, 800 km (500 miles) east of Moscow.

Asked to comment on Asapov's case, the Kremlin said it had no information and suggested sending questions to the defense ministry. The ministry did not reply to a request for comment.

Three rebels said Asapov was not the first general seconded to be their leader, and that there continues to be a rotation of Russians in charge of the rebel army.

Asked whether the defense ministry of the Donetsk republic plays any military role, a senior separatist officer told Reuters: "No. The defense ministry deals only with politics and humanitarian activities."

The rebels who spoke to Reuters asked not to be named because they did not want to be identified giving away secrets.

Asapov's story once again shows a deeper Russian involvement in the conflicts in both Ukraine and Syria than Moscow has been willing to admit. It also shows the inner workings of the strategy of "hybrid warfare", whereby Russia projects power by putting undercover people in command of local forces without publicly risking large numbers of boots on the ground.

Sanctions

Russian President Vladimir Putin himself has said no Russian troops have ever been deployed in Ukraine, not at the beginning of the rebellion in the east and not anytime since.

Asked about instances of Russian servicemen captured in the former Soviet republic, Putin said in one case that a group crossed the Russian border into the country by accident.

In a second case, he conceded that those captured may have included "people who dealt with certain issues including in military sphere", but added: "that does not mean we have regular Russian troops there."

Based on the accounts of Russian servicemen, their relatives and witnesses, Reuters has reported on Russian regular troops entering eastern Ukraine at least twice amid fierce fighting in late August 2014 and around the time of the battle for Debaltseve in the Donetsk region in February 2015.

Kiev and the West say Russia invaded eastern Ukraine and have imposed sanctions on Russia and on individuals believed to have been involved in the conflict and the earlier annexation of Crimea.

The Ukraine government's sanctions list includes more than a thousand Russian and Ukrainian citizens, including Russian military officers. Based mostly on intelligence from Ukrainian agencies, it is difficult to verify independently without Russia's cooperation.

Asapov's name was added in 2016, labeled by Ukrainian intelligence as a "war criminal" for his senior position in the separatist forces. A Ukrainian soldier observes Russian-backed separatist lines in Avdiivka in April 2017. Daniel Brown/Business Insider

At the time of his Ukraine mission, Asapov was formally based in the southern Russian city of Rostov-on-Don, 60 km (37 miles) from the Ukrainian border, according to a 2015 media report noting his transfer and court documents related to his request that family members be named in his dossier so that they could be eligible for privileges attendant on his rank.

Near the end of his official assignment in Rostov in the summer of 2016, Putin gave him the rank of lieutenant-general, according to a decree published online.

When he showed up in Ukraine, Asapov wore a uniform without insignia, said one of the separatists who met him at the time.

When he was formally introduced to the fighters, "we were told our commander had arrived," the senior officer said.

Many rebel officers knew Asapov was a Russian general without being told, he said.

"It was clear anyway... If Russia sends aid, ammunition here, they need to watch it so that this wouldn't be embezzled," he said.

The officer saw that Asapov signed documents as Primakov, and only learned his real name when he saw his pictures in reports about his death in Syria.

Another of the rebels recognized him only after a Reuters reporter showed him a picture of his portrait at his grave.

The separatists' command denies Asapov was in Ukraine.

"Asapov wasn't in Donbass (eastern Ukraine) for sure," Eduard Basurin, a deputy commander and a spokesman of rebel forces, told Reuters.

A Reuters reporter saw Basurin at Asapov's funeral, however. Basurin said he met the general in Moscow in the spring of 2015.

Training While Russia's role in Syria is public, the depth of its involvement has also been obscured. Officially, it conducts air strikes in support of the Damascus government and has a limited presence of special forces and military advisers on the ground.

Asapov's official role in Syria was chief military adviser, according to the defense ministry announcement of his death.

At his funeral, Russia's military chief of staff Valery Gerasimov said he was commander of Syria's Fifth Attack Troop Corps of volunteers.

The corps was introduced by the government at the end of 2016 as a new force that would end attacks against Damascus but has not been heard of since..

The military importance of such "volunteer" units in both Ukraine and Syria is unclear. In Ukraine, Asapov appeared to focus on training, the senior rebel officer said - when he arrived in 2015, most of the fierce fighting was over.

He traveled to military installations from his headquarters in Bosse in southern Donetsk and requested daily reports about the situation on the ground, according to the officer, who did a few of the reports.

He also secured supplies - after his arrival many local recruits were issued new uniforms, which they earlier had to buy, the rebel officer said. Two small Ukrainian separatist flags are seen near a portrait of Russian General Valery Asapov on his grave at a military cemetery near Moscow, Russia October 3, 2017. Reuters

The general also ran the launch of a firing range on a field near the town of Torez, recently renamed Chistyakove, according to four separatists, including two who worked at the range. At the same range he organized a competition among tank crews, a so-called Tank Biathlon, popularized by the Russian military.

Vyacheslav Asapov said he was told his brother was on the frontline coordinating Syrian forces when he was killed by a shell, aged 51. He died on the spot, along with his translator.

He said Valery looked tired when they met for the last time during a short break between stints in Syria last June.

"I don't think anyone is eager to go there. Neither was he," Vyacheslav said. As for Ukraine, "What was there to say? He didn't talk about it much."

Asapov was buried on Sept. 27 with full military honors at the Federal Military Memorial Cemetery outside Moscow. Several days later, two small flags of the pro-Russian separatists appeared on his grave.