The Syrian government accused opposition forces of targeting "the national expertise and intellectuals," The New York Times reported.
Elsewhere, video footage indicated what seemed to be evidence of a new government offensive on the city of Homs, a flashpoint of the year-long uprising against President Bashar Assad, the Times reported.
The shootings in Aleppo, an area that supports Assad, are the latest in an increasingly violent response to the regime's crackdown on protesters, observers said. Earlier this month, a car bomb exploded in Aleppo on the heels of similar attacks in Damascus.
Meanwhile, Belgian officials said the country joined other nations, including the United States, Turkey, European powers and Arab countries, in closing its embassy in Damascus.
"Belgium is closing its embassy in Syria as a result of the deteriorating security situation in Damascus in recent weeks," the Belgian Foreign Ministry said in a statement on its Web site, as well as decreasing the level of diplomatic relations to protest "the continued violence carried out by the Syrian authorities against their own people."
The Local Coordinating Committees, a Syrian activist group, said 26 people were killed across the country by midday Thursday, adding to the more than 9,000 people reported by the United Nations to have been killed since the uprising began a little over a year ago.
The shelling in Homs seemed to contradict assertions that President Assad has accepted a six-point peace plan proposed to him by the special envoy on Syria Kofi Annan, a former secretary-general of the United Nations.
Opposition leaders meeting in Istanbul, Turkey, haven't responded to the news about the peace plan, but expressed skepticism about Assad's apparent acceptance, the Times said.
"We know that there was a initiative of the Arab League and the regime pretended that they agreed but what happened? There are more killings, mass murders and no withdrawal of forces from streets," Walid Banani, a member of the Syrian National Council, said during a news conference in Istanbul.
"So, it's another way of going around and gaining more time," Banani said of Assad's apparent acceptance of the plan. "So we hope that it's not another maneuver by the regime and we lose more lives."