May Iran hardened its tone against a plan to unite Bahrain with Saudi Arabia, calling on its people to protest tomorrow against what it described as a US plot to annex the tiny Gulf archipelago.

The Islamic Propagation Coordination Council, which organises state-backed protests, urged Iranians “to protest against the American plan to annex Bahrain to Saudi Arabia and express their anger against the lackey regimes”. Leaders of the Gulf Cooperation Council (GCC) discussed on Monday plans to turn the bloc into a union, starting with Saudi Arabia and Bahrain.

“This dangerous plot is the result of the American-Zionist-Britain evil triangle to prevent popular uprisings spreading into other countries of the region and to control the internal crisis in Bahrain which has been caused by the inability of the Al-Khalifa regime to control the situation,” the council said on its website.

“Al-Saud and Al-Khalifa should be aware that with this kind of plot they will not stop the popular movement in Bahrain and the movement of Islamic awakening in the region,” it added.

The announcement comes after Tehran warned Riyadh’s plans to form a union with Manama would deepen the crisis in Bahrain, where dozens of people have been killed in violence since Feb 2011.

Saudi Arabia had earlier told Iran to keep out of its relations with Bahrain, a Shiite-majority but Sunni-ruled kingdom. “Any kind of foreign intervention or non-normative plans without respecting people’s vote will only deepen the already existing wounds,” Iranian foreign ministry spokesman Ramin Mehmanparast said.

GCC chief Abdullatif Al-Zayani condemned Iran for making “provocative” comments, saying they revealed “hostile” and “bad intentions” while arousing “anxiety and tension across the region. “Relations between Gulf Cooperation Council states is a Gulf and Arab matter in which Iran has no right to interfere,” Zayani said in a statement.

Iranian MPs had on Monday condemned the planned union between the two Gulf countries. “Bahraini and Saudi rulers must understand that this unwise decision will only strengthen the Bahraini people’s resolve against the forces of occupation,” they said in a letter, referring to the Saudi-led forces.

Bahrain yesterday hit out at Iran for interfering in its affairs. “These statements represent a flagrant interference in the internal affairs of the kingdom and an attack on its sovereignty,” the foreign ministry said in a letter of protest handed to the Islamic republic’s charge d’affairs, according to BNA state news agency.

Saudi-led Gulf forces rolled into Sunni-ruled Bahrain in March 2011 to boost the kingdom’s security forces which a day later crushed month-old, Shiite-dominated protests.

Shiite-dominated Iran has repeatedly voiced support for the protests in Bahrain and strongly condemned the deployment of Saudi-led forces. The GCC was formed in 1981 as the Sunni-dominated monarchies of the Gulf aimed to bolster security after the 1979 Islamic revolution in Iran that was followed by an eight-year war between Baghdad and Tehran.

The Bahrain issue is sensitive one to Iran, where a nationalist-conservative movement within the Islamic regime still considers the island, controlled by Persia before being colonised by Britain and then to gain independence in 1971, as an Iranian province.

“The right is reserved for the Islamic republic, as patron and heir to the territorial integrity of Iran, to want the return of a separated province to the Islamic homeland,” said Hossein Shariatmadari, the director of the hardline Kayhan newspaper.

“The Bahrainis essentially consider themselves to be Iranians and according to some reports they are eager to return to Iran,” he added without specifying on which reports.

Meanwhile, prominent Bahraini rights activist Nabeel Rajab told a court yesterday that a charge that he tweeted insults against the government was “vindictive”, as dozens of lawyers turned up to defend him. “The charge against me is vindictive and is due to my rights activism,” Rajab told a judge at Manama’s Minor Criminal Court, insisting the decision to arrest and try him was political, according to witnesses. “I only practiced my right to free expression. I did not commit a crime. The decision to arrest me and put me on trial was a political decision,” he said.

More than 50 lawyers, both men and women, gathered at the court to defend Rajab, who has been leading protests in the state. The judge adjourned the trial to Sunday, and ordered Rajab to stay behind bars. Rajab, who heads the Bahrain Centre for Human Rights (BCHR), was detained on May 5 for “insulting a statutory body via Twitter”.

He also faces a trial for taking part in a Manama demonstration three months ago. The activist has insisted on demonstrating inside Manama, unlike the main Shiite opposition which now stages its protests in Shiite villages, after last year’s clampdown on protesters who occupied the capital’s Pearl Square for a month.

Despite being a veteran critic of authorities in the Gulf kingdom, Rajab has been spared imprisonment in the wide wave of arrests that targeted activists after security forces quelled the Arab Spring-inspired uprising, possibly for his international exposure and links with rights groups.

Another activist, Abdulhadi Al-Khawaja, who is the former head of the BCHR, has been on a hunger strike in prison since Feb 8. He faces a life sentence among other leading opposition activists. Police fired teargas to disperse several dozen protesters who gathered in the district of Daih on the edge of the Manama yesterday, demanding the release of Rajab and women protesters including Zainab Al-Khawaja, daughter of Abdulhadi Al-Khawaja.

Bahrain also issued arrest warrants yesterday for 20 people accused of injuring policemen and civilians with homemade bombs during months of pro-democracy unrest in the island kingdom.

The interior ministry said it had issued the names and photographs of 20 men, aged 18 to 38, wanted for preparing and detonating “terrorist explosions”. Police say 15 officers have been wounded by three blasts, the first in early April.