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.

Iran warned on Tuesday that Riyadh's plans to form a union with Manama would deepen the crisis in Bahrain, a day after Saudi Arabia told Tehran to keep out of its relations with the tiny Gulf kingdom.

"Any kind of foreign intervention or non-normative plans without respecting people's vote will only deepen the already existing wounds," foreign ministry spokesman Ramin Mehmanparast said in a statement carried by Iranian media.

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.

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.

Victims' families and witnesses on Tuesday accused Iraqi Vice President Tareq al-Hashemi of masterminding killings at the opening of his trial in absentia on charges he says are politically-motivated.

Hashemi, one of the country's top Sunni Arab officials, was accused in December of running a death squad and, along with his staff and bodyguards, faces around 150 charges.

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.

Kuwait's ex-premier Sheikh Nasser Mohammed al-Ahmed Al-Sabah refused to appear before a parliamentary panel probing alleged graft against him, saying the summons issued to him were illegal.

In a letter, a copy of which was seen by Agence France Presse on Tuesday, Sheikh Nasser said the parliamentary panel had no authority to summon a former premier as it can only question ministers and government employees.

At least 24 people were killed in south Yemen on Tuesday, including 12 civilians mistakenly killed in an air raid, sources said, as an army offensive against Al-Qaida militants raged into a fourth straight day.

The civilians died in an air raid on a house in the Al-Qaida stronghold of Jaar, in restive Abyan province, witnesses said.