An attack on a pro-government television station near Damascus killed seven staff on Wednesday, as peace envoy Kofi Annan confirmed a meeting on Syria would be held on the weekend.
Annan also said he will keep Syria ally Iran involved in efforts to halt the conflict even though it has not been invited to Saturday's international meeting in Geneva, UN spokesman Martin Nesirky said.
Annan will "brief" Iran after Saturday's ministerial meeting in Geneva and "will also ensure their continued engagement," Nesirky told reporters.
The UN-Arab League peace envoy said the action group on Syria will meet at the ministerial level, despite wrangling between Moscow and Washington over the terms of reference and guest list.
"The objectives ... are to identify steps and measures to secure full implementation of the six-point plan ... including an immediate cessation of violence in all its forms," Annan said in a statement.
He was referring to his ceasefire plan which was has seen daily violations since it came into effect on April 12.
Among those due to attend are US Secretary of State Hillary Clinton and her Russian counterpart Sergei Lavrov whose country insists that Iran's absence from the meeting could complicate chances for its success.
On the ground at least 61 people were killed in fresh violence across Syria, including the seven staff of Al-Ikhbariya satellite channel and 40 other civilians, the Syrian Observatory for Human Rights reported.
Observatory chief Rami Abdel Rahman told AFP the past week had been the bloodiest since the uprising against President Bashar al-Assad's rule erupted in March 2011.
"The last week was the bloodiest week of the Syrian Revolution," Abdel Rahman said, adding that 916 people were killed from June 20 through 26.
And UN investigators told the UN Human Rights Council in Geneva on Wednesday that sectarian killings are on the rise in Syria and that gross violations of human rights are occurring on a regular basis.
Live footage broadcast by state television showed extensive damage to the studios of Al-Ikhbariya television.
"The terrorist groups stormed the offices of Al-Ikhbariya, planted explosives in the studios and blew them up along with the equipment," Information Minister Omran al-Zohbi said from the scene.
"They carried out the worst massacre against the media, executing journalists and security staff," Zohbi said, adding that a number of staff were kidnapped.
Those killed comprised three journalists and four security guards, state media said. Al-Ikhbariya remained on the air despite Wednesday's assault.
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The United States condemned the attack, echoing remarks made by Amnesty International and press watchdog Reporters Without Borders.
"We condemn all acts of violence including those targeting pro-regime elements," White House spokesman Jay Carney said.
"Even a media organisation engaged in propaganda is still a civilian object, so it and those working for it must never be deliberately targeted," said Amnesty's Middle East and North Africa deputy director Ann Harrison.
Reporters Without Borders said: "News organisations should not be used as targets by the parties to the conflict."
In other violence on Wednesday, 21 soldiers were killed in clashes with rebels and attacks on government forces, including 10 who died before dawn in the eastern province of Deir Ezzor, the Observatory said.
Three rebels also died while 15 troops defected and joined the insurgency, said the watchdog, which reported clashes and shelling of civilian areas across Syria.
On Tuesday, Assad told his cabinet that Syria was in a "real situation of war" and ordered ministers to crush the anti-regime revolt, according to the official SANA news agency.
More than 15,800 people have been killed in the uprising, of whom 4,681 lost their lives since Annan's plan was supposed to take effect on April 12, the Observatory said.
Saturday's talks in Geneva is aimed at shoring up support for Annan's faltering peace plan.
"I look forward to a productive meeting this weekend, where we can all agree on concrete actions to end the cycle of violence and bring peace and stability to the Syrian people," Annan said in a statement.
Clinton said of the Geneva meeting there is "great hope that this perhaps can be a turning point in the very tragic circumstances affecting the Syrian people."
"But we want to make sure any country that participates firmly supports the envoy's transition plan and his original six-point plan," she added.
Diplomats said the United States and European nations had opposed Iran's involvement in the meeting, despite insistance from Moscow that the Islamic republic has a key role to play.
Russian President Vladimir Putin said on Tuesday: "It is better to involve Iran in the settlement (of the Syrian crisis)."