Several emails between American diplomats in Pakistan and their superiors in Washington concerning scheduled drone strikes were forwarded to Hillary Clinton’s unsecured email server, according to a report. The emails are now part of a FBI probe.

Congressional and law enforcement officials briefed on the FBI’s investigation into Clinton’s email use found that the sensitive emails from 2011 and 2012, The Wall Street Journal reported Thursday. The emails were sent to a “computer system for unclassified matters” at the State Department, to give the agency some say in whether the drone strikes would be carried out.

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Some of the emails were forwarded to Clinton, who was serving as Secretary of State at the time and using her private email server, sources told the Journal.

The messages were generally time-sensitive, with the State Department having a narrow window to give input before strikes were carried out. None of the emails, which the Journal described as “vaguely worded,” contained references to the CIA, drones, or any information about the targets, the officials said. They were not included in the Clinton email files released to the public by the State Department.

It is those emails that are now the focus of the FBI investigation into Clinton’s email practices, officials said, which is being carried out to determine if the presumptive Democratic presidential nominee broke US secrecy laws.

Since the drone program is officially secret, sources said that communications with the State Department should have been done over more secure networks, but law enforcement officials told the Journal that they don’t expect charges to result from the mishandling. Several agencies sometimes use less-secure systems to efficiently deal with time-sensitive events, an official told the Journal.

A final review of the evidence will only come after the FBI interviews with Clinton this summer, however.

Clinton’s improper use of a private email server to conduct business as the nation’s top diplomat has become a major headache for her presidential campaign. In late May, the State Department inspector general released a scathing report largely concerning Clinton’s email use, saying that unsecured communications at such a high level created “significant security risks."