Story highlights The remarkable security breach was announced by the president of the Congressional Institute

It's unclear whether the female intruder attended meetings where Trump was present

(CNN) A woman used counterfeit credentials and impersonated a congressional spouse to attend a Republican retreat this week on the same day President Donald Trump, Vice President Mike Pence and British Prime Minister Theresa May met with lawmakers in Philadelphia.

The remarkable security breach was announced by Mark Strand, the president of the Congressional Institute, the nonprofit group that hosted the annual closed gathering. He sent a letter to Republicans on Saturday night alerting them after audio of a panel discussing Obamacare was leaked to The Washington Post and other media outlets.

Most of the policy sessions during the event were attended by members, but spouses were invited to the the lunch with Trump and meeting with Pence, with some posting pictures on social media.

It's unclear whether the female intruder attended those meetings.

Strand's letter stresses that Capitol Police doesn't have the identity of the intruder, but says she went through the same security checkpoints that members and aides did to gain access to the meeting.

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