Syrian President Bashar al-Assad has vowed to purge his country of what he called “terrorists,” as security forces continue to fight rebels who have tried to seize control of parts of Aleppo and Damascus.

Syrian state-run media say Mr. Assad said he would show no leniency towards “terrorists,” following a meeting on Tuesday with Iran's visiting national security council secretary, Saeed Jalili. Syrian state television showed the meeting, the first time Mr. Assad has appeared on television in two weeks.

Jalili pledged continued Iranian support to Syria, which he said was part of an “axis of resistance” against foreign opponents.

Earlier Tuesday, Iran said it was holding the U.S. responsible for the lives of 48 Iranians who were kidnapped by Syrian rebels in Damascus on Saturday.

State-run media say the foreign ministry told the Swiss envoy in Tehran that it expects the U.S. to use its influence to secure the Iranians' release without any preconditions.

Switzerland represents U.S. interests in Iran because Washington and Tehran do not have diplomatic relations. The U.S. has said in the past it is only providing non-lethal assistance to Syrian rebels.

Iran says the 48 abducted were religious pilgrims, but the rebel Free Syrian Army described them as Iranian Revolutionary Guards on a “reconnaissance mission.”

As the two officials met, Syrian forces pounded neighborhoods in the northern city of Aleppo, where the government has been trying to oust rebels from their positions. The London-based opposition Syrian Observatory for Human Rights says at least 12 people were killed in the unrest in Syria's commercial hub.

Meanwhile, U.S. Secretary of State Hillary Clinton says it is time for world powers to begin planning for what will happen after Mr. Assad's regime falls. She commented during a Tuesday appearance with South Africa's foreign minister in Pretoria.

Clinton said she could not predict when the Assad government would fall but was confident that it would. She said she intended to discuss the issue with Turkish officials during her visit to Istanbul on Saturday.

“The intensity of the fighting in Aleppo, the defections, really point out how imperative it is that we come together and work toward a good transition plan.”

Iran's Foreign Minister Ali Akbar Salehi is visiting Turkey on Tuesday to discuss the Syrian crisis with counterpart Ahmet Davutoglu.

The Turkish Foreign Ministry said Tuesday that more than 1,300 Syrians had crossed the border into Turkey over the past day, raising the total number of Syrian refugees in Turkey to nearly 48,000.