The U.N. peacekeeping chief says the Syrian military still has heavy weapons stationed in cities, and that the government and opposition have both violated a peace deal aimed at ending more than a year of unrest.

Herve Ladsous said Tuesday the 24 U.N. observers already in Syria have confirmed there are heavy weapons in several cities, in violation of the peace deal brokered by U.N.-Arab League mediator Kofi Annan.

Ladsous urged both sides to respect the truce.

In violence Tuesday, Syrian activists said fighting in the northeastern province of Deir Ezzor killed 12 soldiers and a civilian. The Britain-based Syrian Observatory for Human Rights also said a mortar shell killed 10 people in the northwestern province of Idlib.

The casualties could not be independently confirmed.

Also Tuesday, a U.N. special envoy said at least 34 children have been killed in Syria since the start of the April 12 agreement brokered by Mr. Annan. Radhika Coomaraswamy urged all parties in Syria to refrain from “indiscriminate tactics resulting in the killing and wounding of children.”

Meanwhile, U.S. President Barack Obama tightened penalties on foreign companies and people who try to circumvent sanctions on Syria and Iran.

Officials at the White House said he signed an order giving the Treasury Department more power to identify those engaging in such activities and to bar them from access to U.S. financial and economic sectors.

Herve Ladsous said the full team of about 300 observers authorized by the U.N. Security Council will be in Syria by the end of this month.

Secretary-General Ban Ki-moon has called for all sides in Syria's 13-month-long conflict to end the violence and cooperate with the U.N. observers to implement the April 12 agreement.

The United Nations estimates at least 9,000 people have been killed since President Bashar al-Assad began cracking down on an uprising against him in March of last year.