(CNN) -- The death toll from fighting between Syrian government forces and civilians rose steadily Sunday as government troops shelled the city of Homs from dusk to dawn, opposition groups said.

At least 43 people, including five children, were killed by security forces Sunday, according to the Local Coordination Committees of Syria, a network of opposition activists. The renewed fighting came a day after the U.N. Security Council failed to approve a plan seeking to halt the violence.

At least 29 of the day's deaths were in Homs, the scene of some of the worst fighting in recent weeks. Opposition groups say more than 300 civilians have died and hundreds have been wounded in the eastern city since Thursday.

An opposition activist in Homs, identified only as "Danny," told CNN that government troops bombarded the city all day with tank fire, mortars and rockets, "which is something new."

"They're not targeting one little place. They're not targeting someone they want. They're targeting everyone," he said.

"If it wasn't for the U.N., they wouldn't have did this," he added. "The U.N. gave them the green light yesterday. It gave them the OK to kill more. If the U.N. had done something about this, this regime would be a little bit scared."

The U.N. Security Council failed on Saturday to pass a resolution aimed at stemming the violence in Syria.

"Danny" said the dead and wounded included children, numbering among them a girl who lost an eye to gunfire and a boy with his jaw shot away. Many of the wounded were being treated in field hospitals in civilian homes, including some who died from wounds that would not have been fatal with proper care.

"We haven't got enough doctors. We haven't got enough medication," he said.

At least six more were killed in Idlib, where gun battles were reported between army defectors and troops still loyal to President Bashar al-Assad. Five more civilian deaths were reported in the Damascus area, with others killed in Daraa and Aleppo, the LCC said.

At least nine government troops died and 21 others were wounded in Idlib, according to the Syrian Observatory for Human Rights, an opposition activist group.

Meanwhile, the state-run Syrian Arab News Agency reported that 15 people -- including two children, an army colonel and eight members of a single family -- were killed by "terrorists" around the country on Sunday. SANA also reported a pipeline was bombed outside Homs.

CNN cannot independently confirm opposition or government reports from Syria because the government has restricted journalists' access to the country.

The Local Coordination Committees announced plans for a two-day civil strike starting Sunday as a way to mount more pressure on al-Assad's government. And the Arab League said Sunday it would continue to work with the Syrian government and opposition to stop the killing urging the government to "heed the people's demands."

Arab League Secretary-General Nabil el-Araby insisted that despite the developments in the Security Council, the Arab League and the international community will continue to seek a resolution to the crisis, according to an Arab League official who could not be named because he is not authorized to speak to the media.

"The Arab League aims to avoid military intervention in Syria and continues to probe for an Arab solution to the Syrian crisis," el-Araby said, according to the official.

The Arab League suspended its mission in Syria a week ago because of a recent sharp escalation in violence, with hundreds killed in clashes. The mission would have monitored whether al-Assad was abiding by an agreement to end the crackdown, which has resulted in an estimated 6,000 deaths, according to the United Nations.

Protesters and rebel fighters have been demanding an end to al-Assad's rule and true democratic elections. Russia and China vetoed a proposed Security Council resolution Saturday that would have demanded al-Assad stop the killing and answer calls aimed at finding a Syrian-led solution to the 11-month crisis.

The other 13 council members voted in favor of the resolution, and U.S. Secretary of State Hillary Clinton called the veto "a travesty" on Sunday.

The veto leaves the world "faced with a neutered Security Council," forcing it to work outside the world body to pressure al-Assad to step down and allow a new government to form, Clinton said.

The Russian and Chinese ambassadors said they support the cessation of violence but did not agree with the text of the resolution, which they said would have complicated the issue and sent conflicting signals to both sides.

Russian Foreign Minister Sergey Lavrov is scheduled to visit Damascus on Tuesday to meet with al-Assad, Russian Ambassador Vitaly Churkin said.

Ambassadors from the three other permanent members of the council -- the United States, France and the United Kingdom -- said were furious at Russia and China for failing to halt the violence that has consumed Syria. U.S. Ambassador Susan Rice told CNN that Russia and China "will have any future blood spill on their hands, while French Ambassador Gerard Araud said Beijing and Moscow have aligned themselves with a regime that is massacring its people.

Syria's U.N. ambassador, Bashar Jaafari, said the crisis has been manufactured and that there is a media campaign to make the Syrian government look bad. The Syrian government has consistently blamed "armed terrorist groups" for the violence.

Referring to the deaths in Homs, Jaafari asked, "Is there a sensible person who would believe a government commits massacres in a given city on a day when the Security Council is scheduled to hold a meeting to examine the situation in that country? Would any entity put itself in such a position?"

CNN's Yousuf Basil, Richard Roth, Mick Krever, Salma Abdelaziz, and journalist Mohamed Fadel Fahmy contributed to this report.