WASHINGTON -- Russia's Foreign Ministry has launched a fresh volley in an increasingly ugly war of words with its U.S. counterparts, calling a former U.S. envoy incompetent and complaining that Washington was pressuring Russian diplomats.

Foreign Ministry spokeswoman Maria Zakharova is known for her caustic remarks, but her June 28 comments, including allegations of high-level "incompetence," were unusually blunt.

U.S. officials have complained in recent weeks that American diplomats in Moscow and elsewhere have been subjected to harassment and increased surveillance.

The public spat comes with U.S.-Russian relations arguably at their lowest point since the Cold War, following sanctions imposed against Russia for its actions in Ukraine and NATO planning an increased military presence near Russian borders.

The Washington Post reported on June 27 that Secretary of State John Kerry had raised the issue of diplomats' treatment with President Vladimir Putin when he visited Moscow in March.

Zakharova complained of U.S. harassment and singled out Michael McFaul, who served as U.S. ambassador to Moscow from 2012-14 and who reported being harassed by Russian security agents and ambushed by state-run TV reporters. McFaul was quoted in The Washington Post article.

She called that article "half-baked" and noted the quotes attributed to McFaul.

"We remember his professional incompetence. McFaul's diplomatic mission fell through with a crash," she said at a briefing in Moscow. "It's possible that it was his efforts that contributed to the worsening of bilateral relations."

One U.S. official recently told RFE/RL that diplomats and their families have been pulled over by traffic police with unusual frequency over the past month and shadowed by Russian security agents to an unusual degree.

"We have raised and we will continue to raise at the highest level any incidents inconsistent with protections guaranteed by international law, and we will respond appropriately in accordance with U.S. and international law," U.S. State Department spokesman Elizabeth Trudeau told reporters on June 27.

Zakharova said: "The United States thinks up ever new restrictions for our diplomats, who are faced with continued provocations by the CIA and the FBI. It repeatedly takes impermissible measures, including psychological pressures, while family members have to watch. In some cases, such actions occurred in the presence of our diplomats' pregnant wives."

In an e-mail to RFE/RL, McFaul, who now teaches at Stanford University in California, said that relations between Washington and Moscow had worsened markedly since he left his post as ambassador. That, he said, made it more perplexing why he continued to be the focus of the Foreign Ministry's ire.

“I'm flattered to think Ms. Zakharova believes I'm so powerful,” he wrote. “Worth noting that the situation in Russia has grown worse since my departure, yet she focused on me. Why? I don't really get it.”

“I worked with some terrific Russian diplomats from the [Foreign Ministry] during five years in the U.S. government. She does not represent them well,” he said.

The issue of surveillance and counterintelligence has also attracted the attention of lawmakers in the U.S. Senate, who have introduced legislation that would impose new restrictions on the travel of Russian diplomats in the United States.

The alleged treatment of U.S. diplomats in Russia has prompted the U.S. State Department to take other measures, including conducting special training sessions on how to watch for and respond to covert and overt surveillance, according to the U.S. official.

The official said other measures seen as pressuring Western diplomats include restricting accreditation for teachers working at one of the main international schools in Moscow, the Anglo-American School. Some teachers are being forced to acquire diplomatic passports, which he said is becoming particularly problematic for British and Canadian teachers at the school.