Some facts about the islands i found in an article,worth reading.
This is link to full article (i suggest you read the whole of it)
The Persian Gulf - Abu Musa & The Tunbs, History and Information
Some of the UAE Arguments: The following two are the main points argued by the United Arab Emirates and Iran's response to them:
1-Priority in occupation:
The first is the argument of "priority in occupation". This claim is vague and ignores the following facts:
A- Whereas the emirates appeared on the political map of
the region only in 19th century, Iran was an ancient nation
and was the only government in the vicinity of these
islands at the time. All historical documents verify that
all islands of northern half of the Persian Gulf have
always belonged to Iran.
B- Ras al-Khaimeh did not exist at the turn of 20th
century, and Sharjah was not, at the time, an emirate of
territorial dimension to be able to claim offshore
territories. The Sheikh was a tribal chief under British
protection, whose authority was to the tribal people
without territorial definition. One should not ignore the
fact that British pretext for taking control in the Persian
Gulf was to suppress the activities of the same tribes,
then referred to by them as "pirates" of no political
entity, let alone territorial dimension.
C- In the nineteenth century, Iran had lease arrangements
with Oman, according to which Fath Ali Shah in 1811 and
Naser ad-Din Shah in 1856 granted the Sultan lease title to
Bandar Abbas, Minab and southern Persian Gulf coastal areas
from east to west as far as Bahrain. If all these areas
belonged to Iran, the islands of Abu Musa and the two Tunbs
situated in its geographical centre could not have been
"unoccupied".
D- Iran's sovereignty and ownership of these islands, as
well as all other offshore and inland areas of the country,
were traditionally established without the display of flags
of identity. Marking occupation or ownership of territory
by hoisting flags was a new concept introduced to the
region by European powers.
E- Nevertheless, in 1887 Iran hoisted flags in Sirri and
Abu Musa to mark her ownership of these islands after
dismissing the Qasemi deputy governors of Bandar Lengeh.
F- Geographical documents from Arab & Islamic historians of
the post-Islamic era confirm that all islands of the
Persian Gulf belonged to Iran.
G- Prime Minister Haji Mirza Aqasi's 1840s proclamation of
Iran's ownership of all islands in the Persian Gulf was not
challenged by any government then or at any time
thereafter.
H- An official British document verifies that after the
establishment of one branch of the Qasemi family at Lengeh,
the family occupied the Iranian islands, probably in the
"confused period subsequent to the death of Nadir Shah".
This story is an admission that Tunbs, Abu Musa and Sirri
islands belonged to Iran and were illegally occupied at a
time when Iran in practice was leaderless.
I- More than 25 official or semi-official British maps of
18th and 19th centuries discovered by this author confirm
Iran's ownership of these islands.
J- Sir E. Beckett, legal expert of British Government at
the Foreign Office (who later served as a judge at the
International Court of Justice) ruled in 1932 that the
Iranians possessed sovereignty over Tamb and Abu Musa in
1887-88.
2-Nineteenth-century correspondence:
Apart from resorting to these old and long exhausted
arguments put forward by the British during the colonial
era, the UAE bases its claims over these islands on a
number of letters exchanged between the Qasemis of Bandar
Lengeh, Sharjah and Ras al-Khaimeh. Some of these letters
date as far back as 1864. They are contradictory and make
fanciful claims on various localities up and down the
region.
The most important of these letters was written by Shaikh
Yusef Al-Qasemi of Bandar Lengeh to the Sheikh of Ras
al-Khaimeh, in which the latter states: "the island of Tunb
actually or in reality is for you". There is little doubt
about the nature of this sentence as a standard oriental
compliment. A few lines below this statement, Shaikh Yusef
adds a further compliment: "and the town of Lengeh is your
town". No one has ever been under any illusion, then or at
any other time, that Port Lengeh had ever belonged to any
country but Iran. When this reference to Lengeh as
belonging to the Sheikh of Ras al-Khaimeh has never been
and cannot be taken as anything other than a
courtesy/compliment, one must ask, how could a similar
reference to Tunb Island be taken literally? Certainly the
expression "mi case es su casa" ought not to be.
When in 1929 King Abdul-Aziz of Saudi Arabia wrote to the
Sheikh of Bahrain complaining about the treatment of his
subjects there, received a letter of from the Sheikh who
states that "Bahrain, Qatif, Hasa and Nejd were all one and
belong to Your Majesty". Certainly inclusion of Bahrain in
that list could not have been but pure compliment.
International Reaction:
International reaction to the UAE claims to the Iranian
owned islands of Abu Musa and the two Tunbs has been one of
impartiality in spite of ten years of campaign by Abu Dhabi
for politicising and internationalising the issue. Despite
the issue of routine statements by the Arab League and the
Arabic countries forming the (Persian) GCC in support of
UAE position, Arab states on the whole remain impartial and
privately apologise to the Iranian authorities for "having
to sign" those statements. This hypocrisy clearly
represents Arab scepticism of these claims, especially at a
time when Arab-Iranian cooperation is high on the political
agenda of both sides in the Persian Gulf.
Of the major powers in the West none has taken side in this
dispute. Politicians from time to time tried to murmur
support for Abu Dhabi but stopped playing games as soon as
they were reminded of their government's impartiality in
the matter. This was particularly true of former UK Foreign
Office Minister, Late Derrick Fatched. He stopped all the
activities he had started in support of Abu Dhabi as soon
as the prominent Iranian scholar and reseracher "Dr. Pirouz
Mojtahedzadeh" wrote and reminded him that it was his
government that negotiated and legally settled the issue of
these islands with Iran in 1971.