Israeli airstrikes on Yemen's Hodeidah port last month appeared to be an "indiscriminate or disproportionate attack on civilians which may amount to a war crime", Human Rights Watch (HRW) said on Monday.
Israel said on July 20 its warplanes struck Houthi military targets near Hodeidah.
The attack targeted oil facilities and a power station and HRW said it killed at least six people and wounded at least 80.
It took place a day after a Houthi drone hit Israel's economic hub Tel Aviv, killing one person, which HRW said also may constitute a war crime.
The retaliatory Israeli airstrikes on Hodeidah hit more than two dozen oil storage tanks and two shipping cranes in the port, as well as a power plant in the province's Salif district, Human Rights Watch said.
"The attacks appeared to cause disproportionate harm to civilians and civilian objects. Serious violations of the laws of war committed willfully, that is deliberately or recklessly, are war crimes."
Analyzed satellite imagery found that the oil tanks burned for at least three days, posing environmental concerns, according to the HRW report.
There was no immediate comment from the Israeli foreign ministry.
Houthi attack
Israel says the Houthis have launched 200 attacks against it since the Gaza war began, many of them intercepted and most of them not deadly.
But a rare Houthi drone strike on July 19 that hit Tel Aviv prompted Israel to announce its first strikes against the group the next day.
The Houthi movement, known formally as Ansar Allah, said it would continue to attack Israel in response.