The Syrian army moved to crush resistance in the Homs region on Monday hoping to free up troops for the north, as Republican challenger Mitt Romney said Washington should be doing more to get the rebels weapons.
Exiled opposition leader Abdel Basset Sayda crossed from Turkey into rebel-held territory in the north for talks with Free Syrian Army commanders on his first such visit since taking up the post in June, rebel sources said.
Turkey bombarded Syrian army positions in response to what Turkish officials said was a new shell strike on a border district, as the military kept up its policy of retaliating for all cross-border fire.
On the ground, the army attacked rebel neighbourhoods of the city of Homs -- Syria's third largest -- and the nearby town of Qusayr, where rebel forces have been under siege since late last year, sources on both sides said.
"The army is in the midst of trying to cleanse the last rebel districts of the city of Homs," a Syrian army commander told AFP.
"The army has already cleansed the villages surrounding Qusayr, and is now trying to take back the town itself," the commander said on condition of anonymity.
A security official told AFP the army hopes to retake the besieged areas by the end of the week to free up troops for battle zones in the north, such as Aleppo.
"It is a huge operation, and we hope to finish it off by the end of this week," the source said, speaking on condition of anonymity.
"After that, we will concentrate on the north of Syria."
Homs province has suffered some of the worst bloodshed and destruction of the uprising which erupted against President Bashar al-Assad's regime in March last year, but since July the main focus of the conflict has shifted to Aleppo, the northern metropolis of some 1.7 million people.
The army pounded a string of rebel-held neighbourhoods in the north and east of Aleppo on Monday.
Hospital staff in just one of those districts -- the Shaar neighbourhood -- told AFP they had received seven dead -- four civilians and three rebel fighters -- and 55 wounded.
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Nationwide, a total of 141 people were killed on Monday -- 56 civilians, 53 soldiers and 32 rebels, the Syrian Observatory for Human Rights said.
The death toll since the start of the uprising now tops 32,000, the Britain-based watchdog said.
In a key foreign policy address on Monday barely four weeks before the US presidential election, Romney accused incumbent Barack Obama of weak leadership in the Syrian crisis which he said was emblematic of an administration that opts to "lead from behind."
"In Syria, I will work with our partners to identify and organise those members of the opposition who share our values and ensure they obtain the arms they need to defeat Assad's tanks, helicopters, and fighter jets," the Republican candidate pledged.
But Romney stepped carefully, refusing to commit any future US government to directly provide weapons to rebels.
Obama, worried that shoulder-fired missiles and other advanced weapons could end up in the hands of terrorists, has not provided arms for the rebel groups, although he has arranged for the delivery of communications equipment.
UN chief Ban Ki-moon called earlier on Monday for a halt to foreign arming of either side.
"I am deeply concerned by the continued flow of arms to both the Syrian government and opposition forces. I urge again those countries providing arms to stop doing so," Ban said.
The Syrian government accuses Turkey and Gulf states Qatar and Saudi Arabia of backing the rebels. The opposition charges that Assad's regime is receiving support from his close ally Iran.
The head of the opposition Syrian National Council held talks with rebel commanders in the town of Bab al-Hawa, just across the border from Turkey, rebel sources said.
Sayda has been attempting to broaden the base of the exiled opposition bloc but only to those groups that back the armed rebellion against Assad's rule.
His crossing into rebel-held territory came with tensions still running high after the shelling of a Turkish border village last week killed five civilians, including a mother and her three children.
A shell from the Syrian side hit the Altinozu district of Turkey's Hatay province on Monday, causing no casualties but sparking a retaliatory bombardment of Syrian army positions, a Turkish official said.