The Saudi authorities say they have arrested 11 Saudis, a Sudanese and an Iraqi linked to Osama Bin Laden's al-Qaeda network who were planning "terrorist" attacks in the kingdom.

The suspects - arrested over several months - were alleged to have been planning attacks on key installations in Saudi Arabia using explosives and surface-to-air missiles, the official SPA news agency said on Tuesday.

The accused will go before an Islamic court for punishment in line with Sharia (Islamic law)

Saudi spokesman

In another development, a sniper wearing camouflage fired five shots at an Australian employee of BAE Systems in northern Saudi Arabia on 5 June, officials said.

The Australian was unhurt in the ambush, near a residential compound in Tabuk, near the border with Jordan.

An Interior Ministry source quoted by SPA said the arrested terror suspects included a Sudanese man believed to be an al-Qaeda cell leader.

He and six Saudis were arrested several months ago.

It is not clear why the arrests have been announced now.

Five Saudis and an Iraqi who had helped hide the Sudanese and smuggle him out of the country were also picked up, SPA reported.

The announcement comes amid US warnings that al-Qaeda is planning more attacks on Western targets around the world.

Morocco said earlier this month that it had arrested three Saudis and three Moroccan women suspected of planning attacks on US and British ships in the Strait of Gibraltar.

Abortive missile attack

On Sunday the Sudanese Government said it had handed the Sudanese suspect over to the Saudi authorities.

He had admitted firing a missile at a US warplane taking off from Prince Sultan Air Base, south of the Saudi capital Riyadh.

Last month Saudi security forces found a missile launcher tube three kilometres (two miles) from a runway at the desert airbase, which is used by about 4,500 US troops.

US officials identified it as a spent casing from a Russian Sam-7 missile, but did not confirm that it was used to target US aircraft.

Another missile of the same type was buried in the desert by the al-Qaeda suspects, the Saudi statement said.

The exiled Saudi opposition says the missiles were smuggled in from Yemen.

Bin Laden campaign

Bin Laden, al-Qaeda's fugitive Saudi-born leader, accuses the United States of insulting Islam by keeping forces in Saudi Arabia.

He has also denounced the Saudi royal family for allowing foreign troops on their soil - home to the holiest shrines in Islam.

The 1996 bombing at Khobar killed 19 US servicemen

Al-Qaeda was blamed for the 11 September terror attacks in the United States. US officials say 15 of the 19 suicide hijackers were Saudi nationals.

According to Dr Rosemary Hollis, a Middle East expert at the Royal Institute of International Affairs in London, the Saudi authorities saw the role of Saudis in the 11 September attacks as highly significant.

Al-Qaeda was seen to be "sending a message to the House of Saud that it had very serious dissidents within" the kingdom, she told BBC News Online.

Islamic militants

In 1996, 19 US servicemen died when a huge truck bomb exploded at the Khobar Towers military base in Saudi Arabia. The US authorities indicted Saudi Islamic militants for the attack.

US intelligence experts say there is mounting evidence that al-Qaeda cells are now functioning largely independently of their leadership.

The BBC's security correspondent Frank Gardner says the Saudi arrests show that al-Qaeda is still alive and operational inside the kingdom - despite previous denials by the Saudi authorities.

The arrests may be connected with those announced earlier in Morocco, and may be based on US intelligence gathered from al-Qaeda suspects held at Camp X-Ray in Cuba, the BBC's Paul Wood says.