U.S. Monitored Manafort After He Left Trump Campaign

U.S. authorities placed Paul Manafort under surveillance after he was ousted as Donald Trump’s campaign manager last summer, according to U.S. officials with knowledge of the matter.

The surveillance, which was part of a counterintelligence investigation into Russian interference with the presidential election, didn’t involve listening to Mr. Manafort’s phone communications in real-time, the officials said.

But armed with a warrant, investigators still could have conducted clandestine surveillance of Mr. Manafort, possibly by obtaining copies of his emails and other electronically stored communications, or by having agents follow him or conduct physical searches of his property.

The surveillance began after Mr. Manafort left the Trump campaign in August, but it is not clear when it was suspended. Mr. Manafort resigned after a spate of publicity about his consulting work in Ukraine on behalf of Russian President Vladimir Putin’s allies.

The government’s focus on Mr. Manafort has grown more intense in recent months. He has become one focus of a probe lead by Special Counsel Robert Mueller, who is examining possible coordination between the Trump campaign and Russia during the campaign as well as whether Mr. Trump obstructed justice when he fired former FBI Director James Comey.

The Russian government and Mr. Trump have denied any wrongdoing.

Mr. Comey’s replacement, FBI Director Christopher Wray, met this week with congressional officials and discussed the law-enforcement agency’s surveillance of Mr. Manafort, according to a person briefed on the discussion.

An FBI spokesman declined to comment on Mr. Wray’s meeting with Congress.

In the face of mounting scrutiny​ and a CNN report that he had been the target of a secret wiretap, ​Mr. Manafort suggested Thursday through a spokesman that he had been caught in the crossfire of the Russia investigation and accused the Obama administration of “pursuing surveillance against a political opponent.”

“It’s unclear if Paul Manafort was the objective,” said Jason Maloni, Mr. Manafort’s spokesman. “Perhaps the real objective was Donald Trump.”

Mr. Manafort, a Republican political consultant, is also being investigated by Mr., Mueller for potential criminal violations of a law that requires foreign agents to register with the Justice Department, The Wall Street Journal has reported.

In piecing together Mr. Manafort’s connections to the Russian government, investigators have reviewed intelligence reports suggesting he was in contact with Russian operatives as early as 2015, according to current and former U.S. officials. In the spring of that year, U.S. spy agencies captured Russian government officials discussing associates of Mr. Trump, including Mr. Manafort, according to the officials.

In some cases, the Russians in the overheard conversations talked about meetings held outside the U.S. involving Russian government officials and Trump business associates or advisers, the current and former officials said.

Those reports could have provided a basis for seeking a warrant to surveil Mr. Manafort, even months after the conversations occurred, if they indicated he was working on the Russian government’s behalf, one official said.

More recently, Mr. Mueller has been investigating Mr. Manafort for possible money laundering, according to a person familiar with the matter. In July, agents for Mr. Mueller served a search warrant on Mr. Manafort’s Virginia home, obtaining documents and other material tied to foreign bank accounts and tax matters, according to people familiar with the raid.

Mr. Maloni said he had no idea if a warrant had been issued against Mr. Manafort. Earlier this week, CNN reported that investigators had obtained a warrant under the Foreign Intelligence Surveillance Act, or FISA, which allows the government to monitor the communications of suspected spies and foreign agents.

Those warrants are classified, and if one were issued, “it is shocking, shocking that someone would reveal its existence,” Mr. Maloni said. He repeated Mr. Manafort’s earlier insistence that “there is nothing to the allegations he is connected to colluding with the Russian government to undermine the 2016 elections.”

According to a January report from the U.S. intelligence agencies, Russia’s interference was directed at the highest levels of its government. Its tactics included hacking state election systems; infiltrating and leaking information from party committees and political strategists; and disseminating through social media and other outlets negative stories about Democratic nominee Hillary Clinton and positive ones about Mr. Trump, the report said.

Del Quentin Wilber contributed to this article