MOSCOW >> President Vladimir Putin vowed Wednesday to push back Ukrainian forces to reduce the threat of attacks on Russian territory as he met with activists running his campaign ahead of the March presidential election that he’s all but certain to win.

Asked about plans for the military campaign in Ukraine, Putin said the line of contact needs to be pushed back to “such a distance from our territory that will make it safe from Western-supplied long-range artillery that Ukrainian authorities use for shelling peaceful cities.”

He added the Russian military has been doing just that, “pushing the enemy back from vital populated centers.”

“This is the main motive for our guys who are fighting and risking their lives there — to protect the Motherland, to protect our people,” he added.

Ukraine has struck inside Russia recently, including a Dec. 30 attack on the border city of Belgorod that killed 25 people, injured over 100.

Putin also said Russian investigators concluded that Ukraine used U.S.-supplied Patriot air defense systems to shoot down a Russian military transport plane in the Belgorod region on Jan. 24. Russian authorities said the crash killed all 74 people onboard, including 65 Ukrainian POWs heading for a swap.

Ukrainian officials didn’t deny the plane’s downing but didn’t take responsibility and called for an international investigation.

Putin said Russia wouldn’t just welcome but would “insist” on an international inquiry on what he described as a “crime” by Ukraine.

Putin, 71, who is running as an independent candidate, relies on a tight control over Russia’s political system that he has established during 24 years in power.

With prominent critics who could challenge him either jailed or living abroad and most independent media banned, his reelection in the March 15-17 presidential vote is all but assured.

“Russia has been forced to defend its interests, including by military means,” Putin told the meeting with his campaign staff, saying that even as the meeting was going on, Russian troops made new gains on the edge of the town of Avdiivka in eastern Ukraine.

“We are passing through a very difficult and important period in the development of our country, the strengthening of its independence and sovereignty in all vectors,” he said. “Scum that is always present is being washed away bit by bit.”

Under a constitutional reform that he engineered, Putin is eligible to seek two more six-year terms, potentially allowing him to remain in power until 2036. He is already the longest-serving Kremlin leader since Soviet dictator Josef Stalin, who died in 1953.

Three other candidates who were nominated by parties represented in parliament are also running: Nikolai Kharitonov of the Communist Party, Leonid Slutsky of the nationalist Liberal Democratic Party and Vladislav Davankov of the New People Party.

All three parties have been largely supportive of the Kremlin’s policies. Kharitonov ran against Putin in 2004, finishing a distant second.

Boris Nadezhdin, a 60-year-old local legislator in a town near Moscow, also is seeking to run. He has openly called for a halt to the conflict in Ukraine and starting a dialogue with the West.

Thousands of Russians across the country signed petitions in support of Nadezhdin’s candidacy, an unusual show of opposition sympathies in the rigidly controlled political landscape that raises a challenge for the Kremlin. On Wednesday, Nadezhdin submitted 105,000 signatures to the Central Election Commission, which is expected to review them over the next few days.