The number of victims rose to 2,237 in 2017, a 19 percent increase from the 1,875 killed in 2014, said James Alan Fox, a criminologist and professor of criminal justice at Northeastern University and an author of the research. The majority of the victims in 2017 were women, a total of 1,527.

Overall, gun-related domestic killings increased 26 percent from 2010 to 2017, which Fox said was cause for alarm. In 2017, 926 of the 1,527 women murdered by partners were killed with guns. In 2014, it was 752 of 1,321 women.

The study, co-written with a colleague, Emma E. Fridel, and published last month, used data obtained from the FBI. It was first reported by HuffPost.

Fox said he could not explain why homicides by romantic partners had risen and wondered if the increase was an anomaly. “I hope it is,” he said. “But I am fearful that it might not be.”

He said stricter gun laws were needed to stem further increases.

“There are states that do a better job than others,” he said. “But the federal government has to step in, too.”

The House of Representatives recently reauthorized the Violence Against Women Act, a law passed in 1994 that is meant to help protect victims of sexual and domestic violence, adding stricter provisions regarding domestic abusers and gun ownership. In particular, the new provisions would close the “boyfriend loophole” and bar those under a restraining order or who were convicted of abusing, assaulting or stalking a domestic partner from buying guns.

The National Rifle Association opposed the legislation. The House bill has not been voted on by the Senate.

Fox said the results of his and Fridel’s research were surprising given a decadeslong slide in such homicides. In 1976, he said, 3,275 people were murdered by a romantic partner, well above the 2017 total. He attributed the decline in recent years to fewer and later marriages, an increase in divorce, and women escaping bad relationships by going to shelters or seeking help.

“Women didn’t have to pick up a loaded gun to get out of a situation,” Fox said.

However, he said, these factors benefited men, mostly, as the number of deaths among them dropped steadily.

“This is information we have to pay attention to,” he added. “It can’t be ignored.”