A senior Iranian official said Wednesday that those backing "terrorist" groups are responsible for the fighting and killings in Syria, as he repeated Tehran's support of the Syrian regime.

"Iran believes that the cause of the Syrian crisis is the sending of arms to terrorist groups into Syria by some countries," Amir Hussein Abdullahian, the Iranian foreign ministry's undersecretary for Arab and African affairs, told a press conference in Kuwait.

British Ambassador to Lebanon Tom Fletcher welcomed on Wednesday efforts among various Lebanese political parties to reach an agreement over a new parliamentary electoral law.

He said: “I welcomed ongoing and constructive efforts to secure agreement on a new electoral law. But the clock is ticking - it is important that the constitutional timetable is respected.”

Syria's opposition Wednesday accused the Damascus regime of exploiting "global inaction" to carry out crimes against humanity, such as the slaughter of nearly 80 men in the battlefront city of Aleppo.

The Syrian National Coalition, the main opposition alliance, in a statement called on international rights groups to investigate Tuesday's massacre in the northern city of Aleppo and "bring the killers to justice."

International donors on Wednesday pledged more than the targeted $1.5 billion in aid for stricken Syrians, U.N. chief Ban Ki-moon said, warning of a "catastrophic" situation in the war-torn country.

"I am pleased to announce that pledges have exceeded the target... more than $1.5 billion have been pledged including the $184 million pledged by non-governmental organizations," Ban told a news conference in Kuwait.

President Michel Suleiman urged donors on Wednesday to provide Lebanon with $370 million assistance for refugees from Syria and called for countries to take in some of the displaced after ringing the alarm bell.

The government has approved a $370 million comprehensive plan for the refugees - $180 for Lebanese state institutions and $190 for international agencies, he told the International Humanitarian Pledging Conference for Syria held in Kuwait.

The Syrian opposition on Tuesday told French senators that it wanted arms but no foreign intervention in Syria, a Senate committee said after a hearing.

"The delegation said it was disappointed by the global community's lack of support and stressed the need for it to receive weapons to wage an effective fight, which isn't currently possible," the foreign affairs and defense committee said in a statement.

Non-governmental charity organizations, meeting Tuesday in Kuwait ahead of a major donors conference, pledged $182 million for Syrian civilians affected by the deadly conflict.

The announcement was made during the meeting hosted by the International Islamic Charitable Organization (IICO) of Kuwait, the official KUNA news agency reported.

Syrian rebels captured early Tuesday a vital bridge across the Euphrates river in the eastern city of Deir Ezzor that could cut off regime supplies to the adjoining province of Hasakeh, a watchdog said.

The Syrian Observatory for Human Rights said the seizing of the Siyasiyeh bridge and another smaller bridge in Deir Ezzor triggered retaliatory air strikes from the regime forces targeting the two crossings.

More than 700,000 Syrian refugees have registered or are awaiting registration in neighboring countries as the conflict in their war-torn nation spirals further out of control, the U.N.'s refugee agency said Tuesday.

"We've had a huge push in the last few weeks. The needs are enormous," UNHCR spokeswoman Sybella Wilkes told Agence France Presse, adding that a colleague on the ground had complained that "we cannot get to everyone fast enough."

At the peak of Iraq's sectarian war, officials in Baghdad accused Syrian President Bashar Assad's regime of allowing Islamist militants to cross the two countries' border to sow chaos.

Now, Damascus may be feeling the consequences of "playing with fire" as the uprising against Assad's rule enters its 23rd month and regime forces fight the Al-Nusra Front -- a formidable group that has been linked to al-Qaieda in Iraq.