A map about Arabs and Arabic speakers (including Iran):
Out dated Iranian gov. sources (and CIA sources) give a roughly estimate of 1-2 million (2-3% of the entire population). Some extremist Arab groups (particularly Ahwazis) represent the other side of the extreme, claiming there are 10 million Arabs in Iran. The truth seems to be somewhere in the middle (or close to it), for according to some independant sources there is an estimate of 3-5 million Arabs living inside Iran.
1. The Arabs of the coastal areas of Iran (Arab as-Sahel/ عرب الساحل)
The Arabs of the coastal regions of Iran (Bushehr and Hormozgan): are relatively small in number (a few hundred thousand) for the majority of the Sunnis (Shafi’is) of the south are the native (Lari/Achomi) Persian Sunnis. However, traditionally some coastal areas (since the arrival of Islam) of the south were inhabited by Arab tribes who without exception are (Shafi’i) Sunnis (unlike the Ahwazi Arabs who are majority Shia).
Many major tribes of the Arabian peninsula migreated (mostly after the arrival of Islam) to the southern Iranian shores, including Bani Tamim, Bani Hammad, al-Maraziq (Marzuqis), al-Qawasim (the rulers of UAE) etc. during some periods of history some of those tribes even had their own emirates in the coastal areas of Iran. Culturally there is almost zero difference between Iranian coastal Arabs and the Arabs in the Gulf countries. Men and women traditional dresses, accent and dialects, custom etc. are all similar to identical, in some southern Iranian towns one could think of himself to be in Bahrain or the Emirates instead of Iran. Gulf Arabic is spoken by southern Iranians Arabs (resembles Emirati Arabic the most) and many Persian Sunnis.
2. Ahwazi Arabs
Khuzestan was formerly known as ‘Arabistan’ (the land of Arabs), for obvious reasons ( most of it southern parts are populated by Arabs). Even the Safavids right up to the Qajar dynasty called this area ‘Arabistan’ (whereas in Arabic it’s known as ‘al-Ahwaz’). It was the Pahlavi dynasty, starting with Reza Pahlavi who changed the name of this region including many Arab cities into Persian ones. Interestingly the Iranian regime that claims Islam also followed the footsteps of the chauvinist Pahlavis, in fact the Iranian regime is even more aggressive in its ‘Persianisation’ politics than the previous regime. Arabistan was a semi-autonomous sheikhdom until 1925, when it was brought under central Iranian government control and later renamed, marking the start of a systematic campaign to Persianise if not obliterate the Arabs of Arabistan (them being Shias didnt help them a lot, for the deep grudge the Iranian Shia regime holds for Arabs is based on the Shia religion itself, hence the support to Palestinians and other Arabs groups are for the sake of propaganda and a certain agenda Iran follows, any Ahwazi Arab can tell a story how Iran would treat Arabs once they are fully under their control, see the killings in Syria were Iran aided an Alawite regime to kill thousands of Arabs).
The Arab (particularly Ahwazi) presence in Iran did not begin with the Islamic conquest of Persia in 633 AD. For centuries, Iranian rulers had maintained contacts with Arabs outside their borders, dealt with Arab subjects and client states in Iraq, and settled Arab tribesmen in various parts of the Iranian plateau. Extremist Persian nationalist groups claim that Ahwazi Arabs are recent immigrants, or at best Arab tribes who settled in Persia after the arrival of Islam. This is not true and contradicts historical accounts which state that Arab tribes have been settled in this very area (including Iraq) thousand of years BC. Arab Ahwazis are not ‘Persianised Arabs’ (except a very small minority), most Ahwazi Arabs trace their origin back to well known Arabic tribes, from the Bani Kaab, Ban Turuf to Bani Tamim. All Arab customs and traditions can be found among Ahwazi Arabs, from the dressing to traditional music.
Ahwazi Arabs (like the absolute majority of Iranian Arabs) are bilingual, speaking Arabic as their mother tongue, and Persian as a second language. The variety of Arabic spoken in the province is Khuzestani Arabic, which is a Mesopotamian dialect shared by Arabs across the border in Iraq and Kuwait. It can be easily understood by other Arabic-speakers. Apparently it resembles the Basrah (Basrawi) accent the most, both accent (Ahwazi and Basrawi are heavily influenced by Farsi (Persian).
Most Ahwazi Arabs are Shias (like southern Iraqis), however, just like southern Iraq has a Sunni minority (in almost ever Shia city, like Basrah etc.), the Ahwazi Arabs too traditionally have a small Sunni minority. In addition to that, the recent mass-conversions from Shiism to Sunnism (even with fear acknowledged by the Iranian regime) have massily increased the number of Sunnis in this region, no other Shia regime of Iran has witnessed mass-conversions like in Khuzestan/Arabistan (although the new phenomenon of conversions from Shiism to Sunnism is known in all of Iran, particularly amongst Persian Shias).
3. Khorassani Arabs
A quite unknown groups. The Arabs in Khorasan are a group of Arabs who immigrated to Khorasan Province, Iran, during the Abbasid Caliphate (750−1513).
Most Khorasani Arabs belong to the tribes of Sheybani, Zangooyi, Mishmast, Khozaima, and Azdi, Khaz’al etc. Khorasan Arabs are Persian speakers, and only a few speak Arabic as their mother tongue. The cities of Birjand, Mashhad, and Nishapur are home to large groups of Khorasan Arabs. Amongst them are Sunnis and Shias.
4. Khamseh Arabs
Khamseh nomads live in eastern Fars Province. The Khamseh is a tribal confederation in the province of Fars in southwestern Iran. It consists of five tribes, hence its name Khamseh, “the five”. The tribes are still partly nomadic, and some are Arabic speaking. They are sheep breeders, which they herd mounted on camels.
The history of the Khamseh confederation of tribes starts in 1861–1862 when Shah Naser ed-Din created the Khamseh Tribal Confederation. He combined five existing nomadic tribes, the Arab, Nafar, Baharlu, Inalu, and the Basseri and placed them under the control of the Qavam ol-Molk family. The pattern of forcibly uniting tribes was not a new idea, as the Safavid Shahs previously created homogenous Kizilbash confederations to temper the increasing strength of the Qashqai, who were gaining so much power. The Khamseh tribes were a mixture of Turks, Luri, and Arabs, but they all came to be called Arabs in contrast to the Turkic Qashqai.
5. Persian (in some cases other Iranian ethnic group) families with Arab ancestry:
These group are not Arabs are neither by themselves nor others inside Iran considered as Arabs, neither linguistically, nor culturally nor traditionally, however as a matter of fact , many Arab tribes, particularly in pre-Safavid Persia have been settled in all major Persian cities, including Shiraz, Isfahan and Ray (Tehran). Therefore it is much likely that many Persian families are descendants of Arab tribes or at least mixed. In fact many Iranian (Persian, Azeri and other ethnic groups) families carry names of Arab tribes such as Banu ‘Amer (Ameris) etc.
Then there are the Shia (and Sunni) Sayyids ( Sadah – سادة) , both claiming ancestry to the Prophet Muhammad (peace be upon him). The authenticity of all those claims can certainly be disputed, for many claimants do not even carry a family tree, however, historically many of the Alawites have settled in Iran, from Mazandaran (Tabaristan in the north) to the Abbasids who ruled Persia and settled in Khorassan and later in the Fars province. It is hence not unlikely that some Persians are descendants of the Quraysh (or even the Prophet Muhammad directly), Sunnis and Shias alike (there are Sunni and Shia Sayyids inside Iran) for intermarriages between the Alawites, Abbasids and other Arab tribes and the Persians did occur.