UPDATE 1-Iran says Saudi Arabia exploring in banned border areas

* Riyadh accused Iran of encroaching on its oil, gas fields

* Tensions over Gulf boundaries, Saudi Shi'ite unrest, Syria

DUBAI, Nov 20 (Reuters) - Iran accused Saudi Arabia on

Tuesday of conducting exploration activities in prohibited

border areas, hitting back at its major rival for regional

influence after Riyadh complained of Iranian encroachments on

its oil and gas fields in the Gulf.

Separated by 250 km (150 miles) of Gulf waters, Shi'ite

Muslim power Iran and Sunni Muslim-led Saudi Arabia have tense

relations. Riyadh accuses Iran of fomenting unrest among

Shi'ites in its oil-rich Eastern Province, a charge Iran denies,

and the two support opposite sides in Syria's civil war.

"Apparently Saudi Arabia has taken action for exploration

activities in prohibited border areas," Iranian Foreign Ministry

spokesman Ramin Mehmanparast said at his weekly news conference

in Tehran, according to the official news agency IRNA.

"The necessary notices were given, and our country's point

of view and our commitment to border agreements were conveyed to

the Saudi ambassador in Tehran."

Mehmanparast was responding to a question about a Saudi

complaint to the United Nations last week saying that Iran

strayed onto its territory near oil and gas fields in the Gulf.

"We think that any differences can be solved in an

environment of cooperation and with a spirit of partnership and

understanding," Mehmanparast added.

The Saudi ambassador to the United Nations, Abdullah

al-Mualimi, was quoted in the daily newspaper Okaz last week as

saying he had sent a letter to U.N. Secretary General Ban

Ki-moon that "details Iran's breaches of the official

conventions and treaties between it and Saudi Arabia".

INTERCEPTION AT SEA

The letter said two Iranian navy boats had intercepted a

vessel belonging to state-owned oil giant Saudi Aramco, and that

Iranian helicopters flew several times over a gas field at

Hasba.

Mehmanparast said it was the Saudis who were at fault.

"The violation that has taken place was on the part of Saudi

companies and if this issue is to be followed up, they must be

questioned," he said. "The discussion about water border limits

between Iran and Saudi Arabia is subject to international laws

and documents between the two countries."

This month, Iran impounded a Saudi Arabian fishing vessel

that entered its southern territorial waters, according to

Iran's official English-language Press TV.

Last month, Saudi border guards arrested 15 Iranians who

tried to enter Saudi Arabia by boat, Saudi media reported.

Iran has had disputes with other Gulf neighbours as well.

Both Tehran and the United Arab Emirates claim as their own

the three islands of Abu Musa and Greater and Lesser Tunb, which

sit near vital oil shipping channels at the mouth of the

strategic Strait of Hormuz.

Iran has said its sovereignty over the islands is

non-negotiable. Mehmanparast was quoted last month as warning

that Iran would consier downgrading ties with the UAE if it

continued to make the claims, although state television later

denied Tehran was considering such a move.

U.S.-backed Saudi Arabia, the world's No. 1 oil producer,

supports the mainly Sunni Muslim rebels fighting to topple

Syrian President Bashar al-Assad. Iran backs the Syrian leader,

whose Alawite religion is derived from Shi'ite Islam.

UNDERSTANDING THE SYRIA CONFLICT