The U.S. warns that civilians face a heightened threat of Russian strikes in coming days.

American intelligence agencies believe Russia is likely to step up its efforts to attack civilian infrastructure and government buildings in Ukraine with the war about to begin its seventh month and Ukraine about to celebrate its Independence Day holiday, the State Department and other U.S. officials said Monday.

The U.S. government declassified an intelligence warning on Monday to ensure that the officials’ concerns about the threat reached a broad audience. Following that declassification, the U.S. Embassy in Kyiv issued a security alert and once more urged American citizens to leave Ukraine.

“The Department of State has information that Russia is stepping up efforts to launch strikes against Ukraine’s civilian infrastructure and government facilities in the coming days,” the alert said. “Russian strikes in Ukraine pose a continued threat to civilians and civilian infrastructure.”

The warning comes as both Ukrainian and American officials have been concerned about a new Russian offensive, potentially timed to Ukraine’s Independence Day on Wednesday and as a response to a string of attacks against Russian military targets in Crimea, the peninsula in the Black Sea that Russia illegally annexed in 2014. The declassified intelligence warning was reported earlier by Reuters.

Throughout the war, Russia has struck civilian infrastructure, including rail lines, shopping malls, auditoriums and apartment buildings. Some of those attacks have been part of broad artillery barrages, while others have been targeted strikes that missed their intended marks.

American officials said the Russian offensive in eastern Ukraine had slowed in recent weeks. Any attacks in coming days are unlikely to be part of a new offensive, officials said.

President Volodymyr Zelensky of Ukraine said on Saturday that Russia could be planning attacks to coincide with Independence Day celebrations, and Ukrainian officials have canceled public events to protect civilians and reduce the number of potential targets for Russia to strike.

“We should be aware that this week Russia may try to do something particularly nasty, something particularly cruel,” Mr. Zelensky said in his nightly address on Saturday.

Mick Mulroy, a former C.I.A. officer and Pentagon official, said he expected Russia to aim for targets in Kyiv, potentially using the killing of Daria Dugina in a car-bombing outside Moscow on Saturday to justify the strikes. Ms. Dugina, 29, was the daughter of Aleksandr Dugin, a political theorist who has provided the intellectual framework for President Vladimir V. Putin’s invasion of Ukraine.

In the months before the Russian invasion in February, the White House began declassifying information about the Kremlin’s plans in an effort to warn Ukrainians and American allies about the threat and to marshal opposition.

While the pace of that declassification has slowed in recent weeks, officials have continued to release synopses of intelligence reports on various Russian plans. The intelligence warnings have continued to prove correct — a signal that American intelligence agencies are still able to collect information on the Russian military’s forthcoming operations.