Tehran blamed regional countries and their "US masters" for the attack on an annual military parade in the city of Ahvaz, but the UAE has denied involvement. A Sunni militant group claimed responsibility for the assault.
Iran summoned Sunday Danish and Dutch ambassadors and the British charge d'affaires over Saturday's attack on a military parade in Ahvaz.
The al-Ahvazieh militant group, a hardline Sunni outfit, claimed responsibility for the attack that killed at least 25 people and wounded more than 60 others.
The Iranian government accused Denmark, the Netherlands and Britain of harboring members of the militant group. They have further made allusions that the attackers were trained in the United Arab Emirates.
Iran's foreign ministry said the fact that the European Union did not blacklist al-Ahvazieh was unacceptable.
The UAE took exception to being implicated in the attack, saying on Sunday that the "formal incitement against the UAE from within Iran is unfortunate, and has escalated after the Ahvaz attack."
Minister of State for Foreign Affairs Emirates Anwar Gargash continued: "The UAE's historical position against terrorism and violence is clear and Tehran's allegations are baseless."
Saturday's attack was carried out by two gunmen on a motorcycle, according to Iran's semi-official Fars news agency.
Rising regional tensions
The attack exposed geopolitical fault lines in the region, with Iran and Saudi Arabia vying for a greater influence in the Middle East.
Tehran accuses Washington of backing Riyadh in the latter's bid for regional supremacy.
Ties between Iran and the US have deteriorated after President Donald Trump restored sanctions on Tehran over its nuclear program.
Iran's Supreme Leader Ayatollah Khamenei said Sunday that the Ahvaz attack was "a conspiracy of US-sponsored regimes in the region," which seek to destabilize Iran.
Iranian Foreign Minister Mohammad Javad Zarif made similar claims on Saturday, accusing regional powers and their "US masters" of being involved in the military parade assault.
"Iran will respond swiftly and decisively in defense of Iranian lives," Zarif wrote on Twitter.
A Revolutionary Guards spokesman alleged the attackers were separatists backed by Saudi Arabia, Iran's regional archrival.
Ahvaz is the capital of Khuzestan province, an oil-rich region where Arab separatists have been known to attack oil pipelines in the past. The province has a large ethnic Arab community, many of them Sunni, the Muslim denomination to which IS adheres and which is a minority in Shiite Iran.
Iran also suffered major attacks by IS extremists on June 7, 2017, when militants assaulted the parliament and the shrine of Ayatollah Ruhollah Khomeini in the capital, Tehran. At least 18 people were killed and more than 50 wounded in the attacks.
shs,es/jlw (AP, dpa)