"The diagnosis is unquestionable: this is SARS," Gennady Onishchenko, Russia's chief epidemiologist, was quoted as saying by the Interfax news agency.
The patient was not identified.
However, Denis Soinikov, who is hospitalized in Blagoveshchensk on the Chinese border, has been undergoing tests for weeks. He was diagnosed with SARS earlier this month, only to have health officials later say they were uncertain.
Onishchenko said a sample of the patient's blood confirmed that he has severe acute respiratory syndrome, which Russians call atypical pneumonia, Russia's Interfax and ITAR-Tass news agency reported.
Russian health officials could not immediately be reached for comment.
Soinikov had been living in a hotel in Blagoveshchensk where about half the residents are Chinese. China has suffered the most cases and the most deaths from SARS.
Russia, which has a long border with China, has closed some border points and initiated mandatory medical exams at others.
In southern China, forestry officials seized game ranging from pheasants to foxes in raids on wildlife markets under new restrictions meant to control SARS, while hundreds of people in Canada were kept under quarantine following a renewed outbreak.
The raids came after a World Health Organization scientist said Tuesday that SARS antibodies found in workers who handled exotic animals at a market in southern China backed the theory that the disease jumped from animals to humans.
The WHO said the emergence of SARS in southern China in November and its spread to more than two dozen countries, infecting more than 8,000 people, has shown that international health regulations need to be updated.
"Here we have SARS illustrating that a public health threat can come out of nowhere," WHO Director-General Gro Brundtland said Tuesday at the agency's annual assembly in Geneva. "The international health regulations are outdated and belong to another time and age."
Authorities in Guangdong banned trade in wildlife this week following suspicions that the virus might have come from animals sometimes eaten by Chinese. Traveling animal shows were ordered to cancel performances, and restaurants that specialize in wild game dishes have been ordered to turn over any live animals.
In the provincial capital of Guangzhou, agents raided four wild animal markets, the Guangzhou Daily newspaper reported on Wednesday. It said they seized 267 pheasants, 54 foxes, 55 pounds of snakes and other wild birds.
In Guangdong, restaurants that serve wildlife — popularly known in China as "wild flavor" — were inspected, along with ports, railway stations, and trucking terminals, the report said.
Animals suspected of carrying disease, including civet cats, monkeys, snakes, and bats must be isolated and checked, said the order published in the provincial newspaper Yangcheng Evening News. In Beijing, the sole farm that raises civet cats for sale to restaurants has been shut down.
China's Health Ministry on Wednesday announced four new SARS deaths and four new cases of infection on the mainland. Beijing accounted for three of the fatalities and three of the cases, the ministry said. The fourth death was in the northeastern province of Jilin. SARS has killed at least 325 people on China's mainland, with more than 5,323 infected.
Taiwan reported five new SARS deaths Wednesday, bringing the global toll to 744. There was also one death reported in Hong Kong.
In the Chinese capital, where officials closed schools and public facilities to prevent SARS' spread and families fled the city, life was starting to return to normal. Traffic accidents jumped 17 percent last week from the week before as drivers returned to the streets. Airlines were restoring flights on the key Beijing-Guangzhou route.
Canada's largest city went back on the WHO's list of SARS-affected places this week following nine new cases and 23 suspected cases linked to hospitals in Toronto.
Still reeling from the biggest SARS outbreak outside of Asia in March and April, Toronto now faces further harm to its crucial convention and tourism industry because of the renewed cases.
Health officials closed a high school north of Toronto late Tuesday and moved to send 1,700 students and staff into quarantine after one student went to Father Michael McGivney Catholic Academy last week showing symptoms of SARS.
The student is considered a suspect case and is in hospital, said Patrick Casey, a spokesman for York Region. The school will be closed until June 3.
Ontario's chief medical officer of health, Dr. Colin D'Cunha, said the number of people quarantined in the province rose to 3,442 Tuesday from about 2,200 on Monday.
An expert from the U.S. Centers for Disease Control and Prevention who went to Taiwan to help with its crisis was rushed back to the United States last week with doctors fearing he himself may have caught SARS.
But preliminary lab results indicate Dr. Chesley L. Richards doesn't have the disease, the agency said Tuesday.
"He continues to be doing very well," agency spokesman Tom Skinner said.