By Khaled Yacoub Oweis and Erika Solomon
ISTANBUL/BEIRUT (Reuters) - Syria's fractious opposition elected a new leader on Saturday but rebel groups were reported to be fighting among themselves in a sign of growing divisions on the ground between factions trying to topple President Bashar al-Assad.
The Syrian National Coalition chose Ahmad Jarba as its president after a close runoff vote that reinforced the influence of Saudi Arabia over a perpetually divided opposition movement that has struggled to convince its Western and Arab allies that its fighters are ready to be given sophisticated foreign weaponry.
Jarba is a tribal figure from the eastern Syrian province of Hasaka who has Saudi connections. He defeated businessman Mustafa Sabbagh, a point man for Qatar, which has seen its influence over the opposition overshadowed by the Saudis.
"A change was needed," Adib Shishakly, a senior official in the coalition, told Reuters after the vote held at an opposition meeting in Istanbul.
"The old leadership of the coalition had failed to offer the Syrian people anything substantial and was preoccupied with internal politics. Ahmad Jarba is willing to work with everybody."
The Muslim Brotherhood, the only organized faction in the Syrian political opposition, has seen its mother organization in Egypt thrown out of power in Cairo this week along with President Mohamed Mursi.
But the Brotherhood representative, Farouq Tayfour, was elected one of two vice-presidents of the Syrian National Coalition in a sign the group still retains influence in Syrian opposition politics.
In northern Syria, rebels clashed with an opposition unit linked to al Qaeda, activists said, in a battle that signals rising tensions between local people and more radical Islamist factions.
Fighting between rebel groups and government forces was reported in Homs and around Damascus in a war whose casualty toll has now topped 100,000.
The rebel infighting comes as forces loyal to Assad have made gains on the battlefield and drawn comfort from the downfall the Muslim Brotherhood in Egypt.
The Islamic State of Iraq and al-Sham (ISIS), a new al Qaeda franchise, has been working to cement power in rebel-held parts of northern Syria in recent months.
ISIS units have begun imposing stricter interpretations of Islamic law and have filmed themselves executing members of rival rebel groups whom they accuse of corruption, and beheading those they say are loyal to Assad.
As hostilities drag on and resources grow scarce, infighting has increased, both among opposition groups and the militias loyal to Assad, leaving civilians trapped in the middle.
The latest internecine clashes were in the town of al-Dana, near the Turkish border, on Friday, local activists said. An opposition group known as the Free Youths of Idlib said dozens of fighters were killed, wounded or imprisoned.
The Syrian Observatory for Human Rights, an opposition monitoring group, said that the bodies of a commander and his brother, from the local Islam Battalion, were found beheaded. Local activists working for the British-based group said the men's heads were found next to a trash bin in a main square.
The exact reasons for the clashes have been hard to pin down, but many rebel groups have been chafing at ISIS's rise in power. It has taken over the once dominant Nusra Front, a more localized group of al Qaeda-linked fighters that had resisted calls by foreign radicals to expand its scope beyond the Syrian revolt to a more regional Islamist mission.
Residents of rebel-held territories in the north once welcomed hardline Islamist groups as better organized and less corrupt. But locals are now growing more wary of them as they impose their austere version of Islamic law.
Protests against radical Islamist groups are becoming more common. The Observatory said the al-Dana clashes were set off at an anti-ISIS protest when some Islamist militants fired at the demonstration.
But other activists said the clashes were more about local power struggles. ISIS units are believed to be buying up land and property, and they also have tried to control supplies of wheat and oil in rebel areas.
Islamist groups that support al Qaeda posted statements on social media saying that they had not started the clashes and had not tried to impose their will on locals.
In Homs, further south, fierce clashes raged as Assad's forces tried to advance in the city, the epicenter of the armed insurgency.
Activists in Homs described air strikes and artillery attacks as a "blitz" and said it was some of the fiercest fighting they had witnessed.
The United Nations estimates between 2,500 and 4,000 civilians are trapped inside Homs.
Some activists decried the National Coalition meetings as a petty power struggle while the battle in Homs raged and appeared to be swinging in favor of Assad's forces.
"How dare the NC have elections and go about its normal business as Homs gets pummeled? History won't be kind to you," said one activist on Twitter, called Nader.
Fighting also took place in two southern districts of the capital, where activists reported rocket and artillery attacks.
The Observatory said that two rockets hit the military's Airforce Intelligence offices in central Damascus. The Airforce Intelligence has long been one of the most feared branches of Assad's secret services.
Heavy air strikes hammered rebel strongholds in eastern suburbs of Damascus, where rebels say the army is imposing a blockade that is choking off their supply of weapons.
(Writing by Giles Elgood; Editing by Robin Pomeroy)