How many people have been killed in Ukraine? Here’s what we know.

In the month since Russia invaded Ukraine, military and civilian casualties have soared. But as the war drags on and the battle lines shift, no one — not even the United Nations, Ukrainian government or U.S. or NATO officials — can provide an accurate count of how many people have been injured or killed.

The few public estimates, including from Western officials, are just that — estimates — and vary widely amid the fog of war. Even the United States and NATO appear to differ over how many Russian troops may have died so far in the fighting. On Wednesday, a senior NATO official told reporters in Brussels that between 7,000 to 15,000 Russian forces have been killed.

The official, who spoke on the condition of anonymity under NATO ground rules, said the alliance estimates that 30,000 to 40,000 Russian troops have been killed, wounded or captured in Ukraine. It’s an estimate, the official said, based on the assumption that for every soldier killed, three are wounded.

But a senior U.S. defense official, who also spoke Wednesday on the condition of anonymity under ground rules set by the Pentagon, said he “had not seen estimates that look like” the numbers released by NATO.

“I would tell you that in the material that I have seen, I have not seen estimates that look like that,” the official said, adding that the United States “continues to have low confidence” even in its own casualty estimates, which earlier this month stood at between 2,000 and 4,000 Russian troops killed. “Because we’re not on the ground, we can’t see, you know, what’s really going on, on a day-to-day basis.”

Russia released just one official casualty update on March 2, when the Defense Ministry said 498 troops have been killed and 1,597 wounded. This week, however, a report that said nearly 10,000 Russian soldiers had been killed in Ukraine — and more than 16,000 wounded — appeared briefly on the website of the pro-Kremlin tabloid Komsomolskaya Pravda. The report was later removed and the paper accused hackers of posting what it said was a “fake insert” and “inaccurate information.”

What’s clear is that Russia’s battlefield losses are real — and that they took many by surprise. Russian President Vladimir Putin had sent more than 100,000 troops to the border with Ukraine for what he thought would be a swift victory allowing his forces to march straight to Kyiv, according to U.S. officials.

But poor logistics and planning, and Ukraine’s surprisingly fierce resistance, buoyed in part by weapons shipments from the West, have helped hobble the Russian leader’s agenda.

“I think they had a bad plan. And I think their logistics support is not what it needs to be,” Lt. Gen. Scott D. Berrier, director of the Defense Intelligence Agency, said of Russia’s military in testimony to House lawmakers this month.

At the same hearing, Director of National Intelligence Avril Haines testified that the war’s human toll was already “considerable, and only increasing.”

For independent observers, the ongoing fighting across much of the country means the effort to count the dead and wounded has become a painstaking but necessary struggle. In Ukraine, as in many war zones, reporting systems have broken down, hospitals and morgues are overwhelmed, and rescuers struggle to retrieve bodies under heavy shelling and intense street battles.

The government, fighting for its survival and also locked in an information war with Russia, has limited access to authoritative information and every incentive to minimize its own losses while emphasizing any victories. It says only 1,300 Ukrainian troops have been killed and denies Russian claims from earlier this month of nearly 3,000 Ukrainian military casualties.

“It’s very difficult to gather good information in the middle of violence because there’s chaos; it’s dangerous to walk around and actually count how many casualties, how many injured, how many killed,” said Charles Kupchan, a senior fellow at the Council on Foreign Relations.

According to the U.N. High Commissioner for Human Rights, which has been tracking civilian casualties, at least 1,035 civilians have been killed and another 1,650 wounded since Russia invaded on Feb. 24. It’s a figure the office concedes is probably a significant undercount. Most of the recorded casualties were caused by the use of explosive weapons “with a wide impact area,” including shelling from artillery and multilaunch rocket systems, as well as missiles and airstrikes, the U.N. said.

Russia’s brutal, sustained bombardments of Ukrainian towns and cities have produced a near-endless stream of images depicting the growing cost of the conflict: an airstrike on a maternity ward; cluster bombs at a preschool; and a trench filled with bodies marking one of the first mass graves. Tales of horror and wanton destruction have emerged from the battered seaside hub of Mariupol, in particular, where a military siege and relentless Russian shelling may have killed thousands of civilians since the war began.

Local officials say that at least 2,400 people have been killed in Mariupol alone, a number that could not be independently verified. U.S. Secretary of State Antony Blinken cited the figure when he announced this week that the United States has formally assessed that Russian forces have committed war crimes in Ukraine.

“We’ve seen numerous credible reports of indiscriminate attacks and attacks deliberately targeting civilians, as well as other atrocities,” Blinken said in a statement. “Every day that Russia’s forces continue their brutal attacks, the number of innocent civilians killed and wounded, including women and children, climbs.”

Tracking those who are killed and corroborating their deaths “is objectively difficult if you’re trying to get it right,” according to Baruch Fischhoff, a professor at Carnegie Mellon University’s Institute for Politics and Strategy.

“The people who are trying to do it are trying to keep themselves alive or trying to keep other people alive,” he said. “Everyone deserves to have their death recorded and honored, and it’s important to know what the scope of the suffering is.”

The Washington Post’s Emily Rauhala in Brussels and Dan Lamothe in Washington contributed to this report, which has been updated.