The opposition Syrian Observatory for Human Rights said an intelligence officer was assassinated Tuesday morning in Damascus, CNN reported.
Activist organizations said government forces assaulted Homs and Hama just days after U.N. monitors left the cities.
Meanwhile U.N.-Arab League envoy Kofi Annan, who developed a six-point peace plan, is expected to brief the U.N. Security Council Tuesday. While only a few U.N. observers are in Syria now, the Security Council recently authorized sending as many as 300 monitors for 90 days.
"It is our hope that the deployment of observers will help to stop the killing and consolidate the calm," said B. Lynn Pascoe, U.N. undersecretary general for political affairs. "The objective, however, is clearly not to freeze the situation but to create the conditions for a serious and credible political process."
The monitors are charged with observing a cease-fire imposed April 12. The cease-fire is part the peace plan laid out by Annan and accepted by Syrian President Bashar Assad's government. Besides calling on both sides to end the violence, the plan calls for access for humanitarian groups, the release of detainees and the beginning of a political dialogue.
Pascoe told the Security Council Monday armed violence in Syria continues and human rights violations are still committed with impunity, CNN reported.
International leaders, including U.S. President Barack Obama, have increased pressure on Assad's regime to end the violent crackdown on pro-democracy protesters that has gone on for more than a year.
Obama signed an executive order authorizing new sanctions the Syrian and Iranian governments and entities that supply new technologies to monitor and track target citizens for human-rights abuses.
European Union foreign ministers agreed to ban exporting goods and technology that might be used by Syria to produce chemical or biological weapons, CNN said.
The European Union also will ban exporting luxury goods to Syria, British Foreign Secretary William Hague said in a statement Monday.
"Despite the urgent need for Assad to end the violence immediately, he and his close supporters continue to lead comfortable lives," Hague said.
Although they voted to increase the observer mission, Russia and China have vetoed U.N. Security Council attempts to take tougher action against the Syrian regime.
U.N. Russian Ambassador Vitaly Churkin defended his country's decisions during an interview with CNN Monday.
"As a matter of principle, we believe that the U.N. Security Council is not about regime change," Churkin said. "We believe that ... if there is crisis in a country, the role of the international community should be to help the parties involved to find a political, peaceful way out of this crisis."
The United Nations estimates at least 9,000 people have died since the protests began in March 2011, Activist groups estimate more than 11,000 people have died.