Iran, the main regional ally of Syria, said on Wednesday that Damascus needs more time to make a U.N.-backed plan aimed at ending 15 months of violence work.

"More time should be given to the Syrian government in order to make (U.N.-Arab League envoy) Kofi Annan's plan a success," Foreign Minister Ali Akbar Salehi said, quoted by ISNA news agency.

Syria's rebels have seen an influx of arms including anti-tank weaponry for their fight against President Bashar Assad regime, in an effort coordinated with the help of the United States, a report said Wednesday.

Officials in President Barack Obama's administration insist it is not directly supplying the weapons or providing funding, with Gulf states paying for the new arms, the Washington Post said, citing U.S. and foreign officials.

Regime troops shot dead at least five people in a new assault on the flashpoint town of Khan Sheikhun and opened fire on a refugee camp in southern Syria on Wednesday, monitors said.

A child, another civilian and three armed militants were killed by machinegun fire in Khan Sheikhun, the Syrian Observatory for Human Rights said.

A convoy of U.N. truce observers came under bomb attack in a Syrian town on Tuesday during a funeral procession in which a monitoring group said regime forces "massacred" 20 people.

The incidents took place as Syria's anti-regime revolt entered a 15th month of relentless violence that has killed more than 12,000 people and amid growing fears that a U.N.-backed peace plan will fail.

People wounded in the crackdown on dissent in Syria, as well as medical personnel trying to treat them, risk arrest and even torture, Doctors Without Borders (Medecins Sans Frontieres) said Tuesday.

"The aim of the Syrian army was clearly to kill the wounded and those suspected of treating them," said one doctor on a team of MSF medics who entered Syria illegally after failing to get permission to work in the country.

Prominent leftist Palestinian writer Salameh Kaileh, freed recently after being arrested in Syria last month, was tortured during his detention, the Syrian Observatory for Human Rights said on Tuesday.

The Britain-based watchdog distributed several photographs showing large bruises and burn marks on Kaileh's arms and legs.

Lebanese national Ali Abu Bakr was killed and several other citizens were hurt on Tuesday when a mortar round fell inside Syrian territory facing the Bekaa border town of Hawsh al-Sayyed Ali, state-run National News Agency reported.

Abu Bakr, a farmer, was cultivating his grove inside Syrian territory when the deadly shell fell during clashes between Syrian forces and rebels.

The United States and 18 other countries have started in Jordan what was described as the largest military exercises in the Middle East in 10 years, focusing on "irregular warfare," top officers said on Tuesday.

"Yesterday we began to apply the skills that we have developed over the last weeks in an irregular warfare scenario ... They will last for approximately the coming two weeks," Major General Ken Tovo, head of the U.S. Special Operations Forces, told reporters in Amman.

Burhan Ghalioun was elected on Tuesday as head of the exiled opposition coalition, the Syrian National Council, an SNC source told AFP.

Ghalioun garnered 21 votes in the leadership battle while another opposition figure, Georges Sabra, won 11 of the 40 votes cast by members of the general secretariat, the source said.

Syria's anti-regime revolt entered its 15th month on Tuesday amid relentless violence that has killed more than 12,000 people and growing fears by Arab countries that a U.N.-backed peace plan will fail.

The Syrian Observatory for Human Rights said another 12 people were killed Tuesday in violence across the country, including four in the coastal city of Banias, a child in Damascus province and five people in the eastern province of Deir al-Zour.