The former US national security adviser John Bolton has said that he will testify in the Senate impeachment trial if he's subpoenaed.

Iran PressAmerica: Bolton is one of several key players who did not appear for any impeachment inquiry hearings in the US House of Representatives.

According to news media, Bolton said on Monday that he is willing to testify in the expected Senate impeachment trial of the president in a surprise development that could complicate a weeks-long dispute over how the trial would play out.

"If the Senate issues a subpoena for my testimony, I am prepared to testify," Bolton said in a prepared statement.

Bolton declined further comment, adding that he came to the decision after 'careful consideration and study'.

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