* Artillery and helicopters attack northwestern town
* Douma residents gather corpses and body parts
* Assad's opponents trade punches in Cairo
By Khaled Yacoub Oweis
YAYLADAGI, Turkey, July 4 (Reuters) - Syrian artillery pounded a northwestern town on Wednesday and areas near the ghost city of Douma, where residents recovered mutilated corpses after a rampage by militiamen loyal to President Bashar al-Assad, activists said.
They said at least 11 people, including a six-year-old girl and an elderly man, were killed by shelling in the towns of Misraba and Rihan near Douma, and three more were shot dead.
Video shot by opposition activists in Douma, 15 km (10 miles) north of Damascus, showed gory scenes in homes they said had been overrun by pro-Assad militiamen after army shelling forced rebel fighters to retreat at the weekend.
The state news agency SANA made no mention of killings in the devastated city, but said utilities had been damaged and that many residents had fled to escape "terrorism".
"These are pieces of our children we're pulling out of dumpsters ... We found these body parts and we are still looking for more. These are burned human body parts," said a man picking through an overturned garbage bin in one of the video clips.
Syrian official curbs on media make it hard to verify accounts of the violence raging on despite diplomacy aimed at preventing an all-out sectarian civil war pitting Assad's minority Alawites against rebellious majority Sunni Muslims.
Opposition leaders and Western governments say more than 15,000 people have already been killed. The government says terrorist gangs have killed several thousand troops and police.
Opposition activists reported an exodus of panicked civilians from the town of Khan Sheikhoun in northwestern Idlib province, but had no precise word on casualties from the bombardment, in which they said helicopter gunships took part.
"They are flattening Khan Sheikhoun," said Mustapha al-Sheikh, a general in the rebel Free Syrian Army (FSA) who is based across the border in Turkey. "Assad is telling the Syrian people: 'Either I will remain or I will burn you'."
Another Syrian general defected to the opposition and fled to Turkey, bringing the number of such renegade generals on Turkish soil to 16, FSA officials said.
Turkey, once an ally of Syria, now hosts some 250 officers who have defected to the FSA in its southern Hatay province and gives them logistical support, but denies arming them.
Turkish-Syrian tensions rose when Syria shot down a Turkish reconnaissance jet over the Mediterranean on June 22.
Turkey's military said on Wednesday it had found the bodies of the F4's two pilots and was trying to retrieve them from the seabed, where the plane's wreckage ended up.
Turkish Defence Minister Ismet Yilmaz said a funeral was planned for them on Friday.
"Yesterday the engine was found. Today other parts are being brought out. All the parts are being taken out bit by bit. We don't want to leave any part there," Yilmaz said.
Syria says the jet was in its airspace when it was shot down. Turkey denies this, although it acknowledges the plane, which it said was unarmed, had earlier violated Syrian airspace.
Ankara has talked tough and has repeatedly scrambled F16 fighters when Syrian helicopters approached the border in the last few days, but it has not retaliated for the shooting down.
Both countries have said they do not want to go to war over the incident, despite their bitter differences over the Syrian uprising against Assad which erupted in March, 2011.
In an interview with Turkish paper Cumhuriyet, Assad said he wished his forces had not downed the jet, but he also accused Turkish Prime Minister Tayyip Erdogan of meddling in Syria.
"With his desire from the beginning to interfere in our internal affairs, unfortunately ... has made Turkey a party to all the bloody acts in Syria," Assad told Cumhuriyet.
Erdogan, once a friend of Assad, now demands he step down and has compared his crackdown with the crimes of Nazi Germany.
The Syrian leader, isolated in the West and the Arab world, can still count on diplomatic support from Russia and China, as well as his longtime Shi'ite ally Iran.
The big powers and several Arab countries agreed at the weekend to promote a political transition in Syria, but disagree on whether this implies Assad and his entourage must step aside, casting a cloud over envoy Kofi Annan's mediation efforts.
British Foreign Secretary William Hague said on Wednesday that Moscow should realise it was futile to keep backing Assad.
"Russia must understand that the situation in Syria is leading to collapse," he told a news conference after meeting his French counterpart Laurent Fabius. "There is no point anybody standing by the Assad regime."
The "Friends of Syria" group meets in Paris on Friday, with U.S. Secretary of State Hillary Clinton and Turkish Foreign Minister Ahmet Davutoglu among those seeking Assad's downfall.
However, the Syrian leader seems determined to fight for survival, given that the West refuses to contemplate military intervention and that Russia and China have twice used their vetoes to block any U.N. Security Council action against him.
Assad's tight-knit, Alawite-dominated inner circle appears to have kept a firm grip on Syria's military and its feared security forces, despite the trickle of army defections.
Syrians trying to end 42 years of Assad family rule have no unified leadership. Opposition groups are fractious and divided, even coming to blows at a meeting in Cairo on Tuesday that had been intended to forge greater unity.
"This is so sad. It will make the Syrian opposition look bad and demoralise the protesters on the ground," activist Gawad al-Khatib, 27, said after a Kurdish walkout provoked fistfights.
(Additional reporting by Erika Solomon and Douglas Hamilton in Beirut, John Irish in Paris, Yasmine Saleh in Cairo and Jonathon Burch in Ankara; Writing by Alistair Lyon; Editing by Andrew Roche)