Iran summoned Bahrain's ambassador in Tehran after his foreign minister told the Islamic republic to stop interfering in his nation's internal affairs, state media reported on Friday.
Foreign Minister Sheikh Khaled bin Ahmad al-Khalifa on Thursday warned Iran to stop meddling over a proposal for Bahrain to form a union with Saudi Arabia.
Tehran "rejects comments made by the Bahrain foreign minister and hopes that the Bahraini government finds a suitable solution towards the developments there," the reports quoted a foreign ministry official as saying.
"The only way out of the existing problems is respond to the legitimate demands of the Bahraini people," the official added.
The planned union between Bahrain and Saudi Arabia, the first part of a broader union of the Gulf's six Arab monarchies, has triggered a war of words between Shiite-dominated Iran and the Sunni rulers of Shiite-majority Bahrain.
The summoning of Bahrain's envoy to Tehran came ahead of Iranian government-organised protests on Friday against what it has called "the American plan to annex Bahrain to Saudi Arabia."
On Thursday, Sheikh Khaled said the union is a "demand by the people" of the Gulf Cooperation Council, while adding that Bahrain "rejects Iranian interference in the affairs of the kingdom."
The minister said that "every once in a while, we hear Iranian claims that Bahrain is the 14th governorate" of the Islamic republic and that Bahrainis want to "return to the motherland."
Saudi Arabia had also previously told Iran to keep out of its relations with Bahrain, where dozens of people, mostly Shiites, have been killed in violence since February 2011.
And Iran hit back on Thursday, with foreign ministry spokesman Ramin Mehmanparast saying "the proposed proposed union or annexation of Bahrain to Saudi Arabia" would lead to the "disappearance" of the Gulf archipelago.
Tensions have escalated between Iran and its Gulf Arab neighbours since a Saudi-led Gulf force rolled into Bahrain in March 2011 to boost the kingdom's security forces which then crushed a month-old Shiite-led uprising against the regime.
Iran has repeatedly voiced support for the protests in Bahrain and strongly condemned the deployment of Saudi-led forces.