* Some soldiers overcome by fumes in tunnels used by rebels -TV
* Bid to deflect blame for nerve gas attack that killed hundreds
* U.N. official in Damascus seeking inspector access to attack site
* Activists say tissue samples being sent to U.N. inspectors
* U.S. repositions naval forces for possible military response
By Oliver Holmes
BEIRUT, Aug 24 (Reuters) - Syrian state television said soldiers found chemical materials on Saturday in tunnels that had been used by rebels, rejecting blame for a nerve gas attack that killed hundreds this week and heightened Western calls for foreign intervention.
The United States said it was realigning naval forces in the Mediterranean to give President Barack Obama the option for an armed strike on Syria and a senior U.N. official arrived in Damascus to seek access for inspectors to the gas attack site.
Syrian opposition accounts that between 500 and well over 1,000 civilians were killed by gas in munitions fired by pro-government forces, and video footage of victims' bodies, have stoked demands abroad for a robust, U.S.-led response after 2-1/2 years of international inaction on Syria's conflict.
In an attempt to strengthen the government's denials of responsibility for the chemical assault in Damascus's embattled suburbs, Syrian TV said soldiers came across chemical agents in rebel tunnels during an advance into the Jobar district.
"Army heroes are entering the tunnels of the terrorists and saw chemical agents," it quoted a "news source" as saying. "In some cases, soldiers are suffocating while entering Jobar. Ambulances came to rescue the people suffocating."
Soldiers discovered a cache of gas masks and imported pills used to ward off exposure to chemical attacks, it said, promising to air footage of "material and drums" later. The report could not be independently confirmed.
State television further accused the rebels of using poison gas "as a last resort after (government forces) achieved big gains during the last few days in Jobar".
Syrian opposition activists say President Bashar al-Assad's forces fired nerve gas projectiles into Jobar and other rebellious suburbs before dawn on Wednesday. Later in the week, activists crossed front lines around Damascus to smuggle out tissue samples from victims of the attack.
The Syrian government and the rebels blamed one another for several previous reported cases of poison gas attacks, both denying responsibility. No independent verification of details has been possible due to a lack of access to battle zones.
Damascus has said it would never deploy chemical weapons against its own citizens, and has suggested rebels may have carried out the latest attack themselves to provoke foreign intervention.
Obama has long been hesitant to intervene in Syria, wary of its position straddling fault lines of wider sectarian conflict in the Middle East, and he reiterated such reluctance on Friday.
But, in a development that could raise pressure on Obama to act, American and European security sources said U.S. and allied intelligence agencies had made a preliminary assessment that chemical weapons were used by pro-Assad forces this week.
Major world powers - including Russia, Assad's main ally which has long blocked U.N.-sponsored intervention against him - have urged the Syrian leader to cooperate with a U.N. inspection team that arrived on Sunday to pursue earlier allegations of chemical weapons assaults in the civil war.
U.N. High Representative for Disarmament Affairs Angela Kane arrived to Damascus on Saturday to press for a Syrian government green light for inspectors to examine areas of Damascus suburbs said to have been targeted on Wednesday.
Assad's government has not said whether it will grant such access despite increasing pressure from the United Nations, Western and Gulf Arab countries and Russia. If confirmed, it would be the world's deadliest chemical attack in decades.
"The solution is obvious. There is a United Nations team on the ground, just a few kilometres away. It must very quickly be allowed to go to the site to carry out the necessary tests without hindrance," French Foreign Minister Laurent Fabius said on Saturday during a visit to the Palestinian territories.
Foreign Minister Guido Westerwelle of Germany said it expected Russia to "raise the pressure on Damascus so that the inspectors can independently investigate".
President Hassan Rouhani of Iran, Assad's most powerful Middle East ally, acknowledged on Saturday for the first time chemical weapons had killed people in Syria and called for the international community to prevent their use.
Washington said on Friday it was repositioning warships in the Mediterranean, although officials cautioned that Obama had made no decision on any military move. A U.S. defence official, speaking on condition of anonymity, said the navy would expand its presence there to four destroyers from three.
U.S. MILITARY OPTIONS
Among the military options under consideration are targeted missile strikes on Syrian units believed responsible for chemical attacks or on Assad's air force and ballistic missile sites, U.S. officials said. Such strikes could be launched from U.S. ships or combat aircraft capable of firing missiles from outside Syrian airspace, thereby avoiding Syrian air defenses.
But the defence official stressed the Navy had received no orders to prepare for any military operations regarding Syria.
Obama called the apparent chemical attack a "big event of grave concern" and one that demanded U.S. attention, but said he was in no rush to get war-weary Americans "mired" in another Middle East conflict.
"If the U.S. goes in and attacks another country without a U.N. mandate and without clear evidence that can be presented, then there are questions in terms of whether international law supports it," he said on Friday. "The notion that the U.S. can somehow solve what is a sectarian complex problem inside of Syria sometimes is overstated."
Obama's caution contrasted with calls for action from NATO allies, including France, Britain and Turkey, where leaders saw little doubt Assad's forces were behind the chemical attack.
While the West accused Assad of a cover-up by preventing the U.N. team from heading out to Damascus suburbs, Russia said the rebels were impeding an inquiry and that Assad would have no interest in using poison gas for fear of foreign intervention.
Igor Morozov, another senior pro-Kremlin lawmaker, told Interfax news agency: "Assad does not look suicidal. He well understands that in this (chemical attack) case, allies would turn away from him and ...opponents would rise. All moral constraints would be discarded regarding outside interference."
Alexei Pushkov, pro-Kremlin chairman of the international affairs committee in Russia's lower house of parliament, said: "In London they are 'convinced' that Assad used chemical weapons, and earlier they were 'convinced' that there were weapons of mass destruction in Iraq. It's the same old story."
Russia said last month that its analysis indicated a deadly projectile that hit a suburb of the Syrian city of Aleppo on March 19 contained the nerve agent sarin and was most likely fired by rebels.
More than two years into a civil war that has divided the Middle East along sectarian lines, the contrasting lines taken by Western governments and Russia on this week's chemical attack highlighted once again the international deadlock that has foiled effective outside efforts to stop the bloodshed. (Additional reporting by Megan Davies in Moscow, John Irish in Paris, Madeline Chambers in Berlin, Yeganeh Torbati in Dubai and Washington bureau; Writing by Mark Heinrich; Editing by Alison Williams)