More than 100 people - most of them civilians - were killed across Syria on Saturday, according to opposition activists, three days before a United Nations-brokered ceasefire is to go into effect, dpa reported.
The Syrian Observatory for Human Rights said 70 civilians, 16 army soldiers and 17 security personnel were killed.
"Forty of the civilians were killed in al-Latmana Hama (province). The others died in the provinces of Homs and Idlib," said Rami Abdel Rahman, the head of the London-based group, referring to key opposition strongholds.
Activists from Hama reported mass executions in the suburb of al-Latmana.
"Young men were lined along the walls and shot," said Saleh al-Hamawi, an activist based in the area.
News from Syria is difficult to verify as the government has barred most foreign media from the restive areas since a pro-democracy uprising erupted in March 2011.
The surge in violence came despite sharp criticism of the Syrian government from UN Secretary General Ban Ki-moon.
In a statement late Friday, Ban deplored the assault by Syrian troops on "innocent civilians, including women and children, despite the commitments by the government of Syria to cease all use of heavy weapons in population centres."
Anas Airout, a member of the opposition Syrian National Council, Saturday warned: "The Syrian regime will intensify attacks in the coming 24 hours to make as many gains as possible on the ground before the April 10 deadline."
He told dpa, "This regime has no mercy. It is bent on killing anyone who dares to say, 'No'. But we tell the regime: 'You will never succeed God willing'."
Syria has said it accepted a peace plan proposed by UN-Arab League envoy Kofi Annan aimed at ending the conflict, in which more than 9,000 have been killed, according to UN estimates.
Annan's plan calls on the regime of President Bashar al-Assad to pull back its troops and heavy weapons from civilian areas, and for all parties, including the opposition, to cease violence within 48 hours of this withdrawal.
It also calls for the release of detainees, access to humanitarian services, and talks between the government and opposition.
The official news agency, SANA, Saturday said Damascus had sent letters to Ban and the president of the UN Security Council, US Ambassador Susan Rice, telling them that "terrorist acts" were on the rise.
"The terrorist acts committed by the armed terrorist groups in Syria have increased in the last few days, particularly after reaching an understanding on Kofi Annan's plan," SANA quoted the letter as saying.
Damascus has demanded a written commitment that the opposition would not take advantage of the withdrawal to make territorial gains, according to SANA.
Meanwhile, a Lebanese bus carrying pilgrims to Iraq was attacked by unknown gunmen near a border crossing with Syria, the Lebanese National News Agency reported Saturday, wounding dozens of passengers.
Lebanese LBC television reported that seven people - six Syrians and one Lebanese - were killed in the attack, when gunmen fired at the bus from the Syrian side of the border at the eastern Al-Jusiyeh crossing, according to the report.
In Syrian capital Damascus, thousands of loyalists of al-Assad demonstrated on Saturday in a show of support to mark the 65th anniversary of the ruling Baath Party.
Similar rallies were held in other cities, according to SANA.
Syrian state media, meanwhile, reported that Foreign Minister Walid al-Moallem was expected to visit Moscow on Monday for talks on the latest developments in the country.
Russia, a main supplier of arms to the Syrian government, has along with China vetoed two UN Security Council resolutions against Damascus.