An EU official, who spoke on the condition of anonymity, told Iran's official news agency IRNA that Mogherini will not be able to attend the conference due to her tight schedule.
Mogherini will be “traveling in those days, hence her attendance is not foreseen,” the official told IRNA’s correspondent in London.
A senior EU official also confirmed IRNA’s report on Thursday, saying Mogherini will not attend the gathering because of a prior engagement, the Wall Street Journal reported.
The meeting is to be held in Poland on February 13-14 as part of US efforts to increase global pressure on the Islamic Republic.
However, ministers from several European Union countries will likely skip the summit, the Wall Street Journal quoted officials as saying.
There is “a lot of uncertainty about participation of many other EU member states at ministerial level,” one official told the newspaper.
European diplomats have said in recent days that France is unlikely to send its foreign minister. The UK and Germany haven't decided who will represent them. Luxembourg’s foreign minister said he would miss the event because of a prior arrangement.
One European diplomat said the bloc will not be “joining an anti-Iran coalition.”
A group of activists in the United States and other countries recently signed a petition, calling on European countries to boycott an anti-Iran summit.
The activists started the petition on the website of the anti-war group Code Pink to ask European countries not to attend the summit.
More than 3,400 people have so far signed the online petition, which urges EU countries to skip Pompeo’s “belligerent conference” and “instead host an alternative one with all nations of the region, including Iran.”
The European Union is a strong supporter of the 2015 Iran nuclear deal and is seeking to help retain economic ties with Tehran despite renewed US sanctions on Iran following US President Donald Trump’s decision in May to withdraw from the accord.
Mogherini has spearheaded EU efforts to sustain the 2015 deal, which offered Iran relief from sanctions in exchange for steps to curb its nuclear program.
The summit, which will be co-hosted by Poland and the US and take place in Warsaw, was announced during Pompeo’s tour of the Middle East last week.
Iran has expressed its strong protest at the planned summit, with Foreign Minister Mohammad Javad Zarif denouncing it as a “desperate anti-Iran circus.”
The Iranian Foreign Ministry also summoned Polish chargé d'affaires in Tehran, Wojciech Unolt, to protest the conference.
"This is a hostile measure by the United States against the Islamic Republic of Iran, and Poland is expected to avoid assisting the US in holding the conference,” an Iranian Foreign Ministry official told Unolt last Sunday.
Unolt provided explanations regarding the upcoming summit and said that it was not against Iran.
"He said Poland’s stance is different from that of the US and does not conform with the recent remarks made by US officials," the agency added.
The Iranian official, however, rejected the explanation as insufficient, saying the Poland government should immediately compensate for the move or have Iran "inevitably take reciprocal measures."