MOSCOW — Russian leader Vladimir Putin triggered a flurry of speculation Thursday when he suggested he was open to a constitutional change that would limit any president to no more than two terms.

In his traditional end-of-year news conference — lasting four hours and 19 minutes — Putin also came down on President Trump’s side in the impeachment battle, said Russia would help China build an early-warning missile defense system and complained that an anti-doping body’s decision barring Russian athletes from international competitions was unfair.

But Putin’s remarks on the constitution generated the most interest. Were they a signal that Putin — who has effectively reigned since 2000 — would not try to seek office when his second presidential term expires in 2024? Or did they suggest that he plans to run again, on the grounds of new rules and a new constitution?

Although Putin was reelected only last year, speculation has focused on whether he plans to cling to power at the end of his term or manage a transition designed to preserve his political legacy — for example, by maneuvering a reliable successor into power.

There seemed little doubt that Putin, choosing his words carefully, intentionally left his true meaning open to interpretation. But after the news conference, he said he had made the remarks off the top of his head in response to a question.

Putin earlier told 1,895 international and Russian journalists that a move to change the constitution was possible, to bar anyone from serving as president for more than two terms. The constitution currently prohibits presidents from serving more than two terms “consecutively.”

Many nations — including China, Egypt, Kazakhstan, Uzbekistan, Uganda, Bolivia and Rwanda — have scrapped or altered presidential term limits. In 2015, Burundi’s Pierre Nkurunziza used the pretext of a new constitution to run for a third term, which led to protests and violence.

Putin served two terms from 2000 to 2008 and then swapped places with his prime minister, Dmitry Medvedev, who served one term. Medvedev was widely seen as a caretaker, enabling Putin to retain power behind the scenes. Then Putin took over the presidency in 2012 and was reelected last year. Under the constitution, he cannot seek office again.

After the news conference, Putin ruled out any hasty decision, adding, “One can’t make quick decisions here. The discussion is underway, and I will watch how it develops.”

Sergei Mironov, leader of the State Duma faction A Just Russia, said Putin’s words indicated that he would not seek reelection.

“The president believes the word ‘consecutive’ could be removed as regards the duration of stay in the post of president. In my view, this shows clearly that Vladimir Putin is not going to stay in this post after 2024,” Mironov told reporters Thursday.

Others viewed Putin’s remarks as a trial balloon, designed to test the waters on the possibility of extending his term.

During the news conference, Putin also said the impeachment case against Trump was a political effort by Democrats to remove the U.S. president from power — but he predicted it would fail because of the Republican majority in the Senate.

“It’s unlikely they will want to remove from power a representative of their party based on what are, in my opinion, completely fabricated reasons,” Putin said. “This is simply a continuation of the intra-political battle where one party that lost an election, the Democratic Party, is trying to achieve results using other methods and means.”

He said the Democrats first accused Trump of colluding with Russia during the 2016 election campaign, though he denied there was any conspiracy. Then, Putin asserted, the Democrats dreamed up the idea that Trump had exerted pressure on Ukraine to advance his personal or political interests.

Putin also complained that Russia was being treated unfairly on the world stage, whether by U.S. legislators who have voted to impose sanctions on companies building a Russian gas pipeline to Germany, or by sporting authorities that have banned Russian athletes from international competitions for four years.

Putin attacked the World Anti-Doping Agency’s ruling as an anti-competitive move designed to shut out Russian stars.

“It’s not fair. It doesn’t make sense, and it runs counter to international law,” Putin said, adding that any punishment should be directed against individuals, not a nation. “If the vast majority of our athletes are clean, how can you slap a ban on them?”

He said that Russia’s figures skaters were geniuses and that the measure seemed directed toward preventing them from winning.

“It’s an attempt to get rid of competition,” he said. “Yes, you can do it. Will it help world sport? No.”

Putin’s annual news conference, as usual, spanned a gamut of topics, including prices for flights from the far east of the country to Moscow, garbage disposal, health care and climate change.

He also warned that if the United States did not endorse a new Strategic Arms Limitation Treaty, the world would be plunged into a new arms race.

Putin also said he welcomed all questions, critical or not.

“I always welcome criticism. It always keeps us on our feet and provides food for thought. It makes us think twice about issues raised,” he said.

The news conference has been a Putin tradition, closely watched as a barometer of Russian foreign and economic policy.

However, Putin does appear at other news conferences during the year — his last such appearance was last week in Paris after talks with Ukrainian President Volodymyr Zelensky and with the French and German leaders, aimed at reviving a stalled peace deal in eastern Ukraine.

This year’s year-end news conference came amid souring U.S.-Russia relations, with Trump likely to sign a bill soon containing sanctions designed to block an important Russian gas pipeline to Germany. The Senate Foreign Relations Committee is advancing a separate bill this week that would impose tough new sanctions on Russia over its 2016 election interference, aggression against Ukraine and other actions.

Putin said the United States cooperated with Russia when it suited its purposes but imposed sanctions to hold Russia back. He warned that Russia would retaliate against any new sanctions, which he described as “completely hostile actions.”

Putin’s domestic approval rating remains high — about 68 percent in July, according to the Levada-Center polling organization — but it has been gradually declining. Russia’s flat economy — with growth at around 1.2 percent, the World Bank reported — has fueled domestic discontent, as have unpopular moves last year to raise the retirement age and increase value-added taxes.

Russia’s economy may be unimpressive, but Putin has amplified Russia’s global influence this past year, homing in on areas where U.S. influence has waned. Russia moved swiftly to fill a vacuum left by the withdrawal of U.S. troops from northern Syria. Putin fostered warm relations with Chinese President Xi Jinping amid the bitter U.S.-China trade war and has reached out to African leaders, hosting an October summit in Sochi that was attended by 45 African heads of state and government.

On Ukraine, he said he was alarmed by Zelensky’s calls for changes to agreements that form the basis of the peace talks. He denied that Russian troops were present in eastern Ukraine, where 13,000 people have died in a separatist war in the past five years.

The format of Thursday’s event was less a news conference than an opportunity for journalists from far-flung regions, often wearing national costumes, to put forward requests or raise hot issues affecting their regions.

One from Bulgaria carried an icon. Another from Mordovia, a region east of Moscow, brought a gift of a local musical instrument, and a journalist from a Moscow suburb called Pavlovsky Posad, known for producing brightly colored shawls, held up a pink one depicting the president. A journalist from Crimea, annexed from Ukraine by Russia in 2014, told Russian television that she was there to raise the matter of water supplies in the region.