Foreign Affairs Minister Simon Coveney says some of his EU counterparts were contacted after his phone was hacked last year.
Minister Coveney says the issue was dealt with swiftly and the hack led to him being more careful about the security of his texts.
The Chair of the Foreign Affairs Committee said the minister still had questions to answer over his texts about the Katherine Zappone UN special envoy appointment.
Minister Coveney's written to Charlie Flanagan to insist any suggestion he was trying to keep his texts to the Tánaiste secret are "plain wrong".
In the letter, Minister Coveney said: "It is already publicly known that my phone was compromised in 2020.
"What is not known is that some of my foreign minister colleagues across Europe were contacted using my phone’s identity as a front during that hacking incident.
"I believe the matter was dealt with swiftly and thoroughly by my department and the Gardai from whom I take ongoing advice.
"As a result of this incident and others, I work on the basis that very few telecommunications are completely secure."
Minister Coveney said he "completely rejects" any suggestion he misled the committee when he appeared before it earlier this week, and has offered to appear before it again to offer any clarity.
It comes after Minister Coveney yesterday said it was "prudent" for him to delete text messages - noting he had been hacked in the past.
Meanwhile, Leo Varadkar has insisted the ongoing saga is not distracting from the work of the Government.
He said he still has the support of his Government colleagues amid the continuing political fallout of the 'Merriongate' controversy.
Mr Varadkar said he and Minister Coveney have apologised for not informing other Government leaders about Ms Zappone's appointment earlier, saying the situation should have been handled better.
