U.S. President Barack Obama and his Russian counterpart Vladimir Putin on Wednesday acknowledged their differences on Syria, but agreed to continue discussions toward a solution, the White House said.

In their conversation over the phone, the two presidents discussed the "developing situation" and the "growing violence" in the Arab nation, agreeing on the need to "support a political transition as soon as possible that achieves our shared goal of ending the violence and avoiding a further deterioration of the situation," the White House said.

"They noted the differences our governments have had on Syria, but agreed to have their teams continue to work toward a solution, " it said.

Due to the lingering differences on approaches to the 16-month crisis in Syria, the UN Security Council decided to postpone until Thursday morning a scheduled vote for Wednesday on a draft resolution concerning Syria.

The West-proposed draft resolution, whose sponsors include France, Germany, Portugal, Britain and the United States, grants extension of the UN Syrian Supervision Mission (UNSMIS) for a period of 45 days and threatens non-military sanctions in case of Syria's non-compliance in pulling out government troops and heavy weapons from populated areas within 10 days.

While Russia, in its own version of draft presented to the Council, asks for extending the mandate of UNSMIS for another three months, reducing the number of military observers and asking the operation to take on a more political mission. It opposes any threat of sanctions against Syria.

Syrian Defense Minister Dawood Rajha and his deputy Assef Shawkat were killed Wednesday morning when a suicide bombing ripped through the country's intelligence headquarters in the capital city of Damascus.

The attack followed three days of violent clashes in the capital between the Syrian government and rebel forces, prompting U.S. Defense Secretary Leon Panetta to declare the situation in Syria "spinning out of control" and call for more international pressure on Damascus.

Washington on Wednesday expanded its sanctions against Syria by covering the prime minister, two deputy prime ministers and 26 ministers as well as six companies.