Halaqi was accompanied by the oil, industry, health and electricity ministers, state news agency IRNA reported, without specifying the duration of the trip.
Tomorrow he will hold talks with Vice President Eshaq Jahangiri, the government's website said.
Halaqi's visit comes one week after Syria's Foreign Minister Walid Muallem held talks in Tehran and said the Islamic republic would back a Russian plan to end his country's more than three-year conflict.
Moscow is hoping to relaunch peace talks for the war-torn country that would include meetings between government officials and members of the opposition.
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De Mistura briefed the European Union on his efforts on the weekend and today the EU said it backs the plan as one of the few good options left in a conflict that has claimed more than 200,000 lives.
The Syrian Observatory for Human Rights said the Syrian army lost control today of the Hamdiyeh and Wadi al-Deif bases in northwestern Idlib province to Al-Qaeda and other Islamist groups.
Tehran also helps bankroll Syria's economy, devastated by sanctions and the fallout from the nearly four-year war, which has also displaced 7.2 million people and forced 3.2 million to flee the country.
Tehran last year offered Damascus two credit lines totalling USD 4.6 billion to pay for imports of energy and wheat.