Syrian activists say at least 43 people have been killed in violence in Syria, just days before a cease-fire is to go into effect.
The London-based Syrian Observatory for Human Rights reported 40 people died in army shelling of areas of Hama and three more in Homs.
Rebels, meanwhile, attacked the Minakh air base, on the outskirts of Aleppo, Syria's third-largest city, opposition activists said.
UN Secretary-General Ban Ki-moon said on April 6 that the continued attacks by Syrian government forces on cities held by, or sympathetic to, opposition groups "violate" an agreement with the UN Security Council on withdrawing troops.
Ban said Syrian President Bashar al-Assad's agreement to halt use of heavy weapons by April 10 "is not an excuse for continued killing" ahead of that deadline.
Ban demanded Syrian authorities immediately end all military operations.
U.S. Ambassador to Syria Robert Ford posted satellite images on Facebook that showed Syrian artillery prepared to shell residential areas and the movement of forces from one city to another.
Ford, who is in the United States now, said, "The regime cannot hide the truth."
Syria has said it accepts the peace plan proposed by international envoy Kofi Annan aimed at ending the conflict, in which more than 9,000 have been killed, according to the UN.
The Annan-brokered deal that calls on all sides in the Syrian conflict to end hostilities by April 10 and start negotiations.
It requires the Syrian government to pull back its troops and heavy weapons from civilian areas, and for all parties, including the opposition, to cease armed violence within 48 hours of this withdrawal.
The plan also calls for the release of detainees, for access to humanitarian services, and talks between the Syrian government and opposition.
The world's largest Islamic body said on April 7 it was preparing to send humanitarian aid worth up to $70 million to help around 1 million people affected by the violence in Syria.
The Organization of Islamic Cooperation (OIC), whose 57 member states include Syria, said it was working on a program with the United Nations to send much-needed food supplies and medical aid.
The move comes after eight UN experts and three from the OIC went on government-led visits inside Syria last month.
The UN says more than a million people affected by events in Syria are in need of urgent humanitarian aid.
According to the UN, more than 9,000 people have been killed in Syria since a crackdown on pro-democracy demonstrators began in March 2011.
With reporting by Reuters, dpa, AFP, and AP