The strength of the Syrian Army has declined from a 220,000 in 2011 to 90,000 in 2016 (according to the International Institute for Strategic Studies). The al-Assad and Iranian governments have also sponsored two pro-government Syrian militias (the National Defense Forces (NDF) and Popular Defense Committees).
Hezbollah provides training for pro-Assad paramilitary groups and has fought against rebel forces, particularly near the Lebanese border. According to the International Institute for Strategic Studies, there are between 4,000 and 8,000 Hezbollah fighters in Syria.
The US, EU, Arab League, Organization of Islamic Cooperation (OIC), and Gulf Cooperation Council (GCC) all consider Hezbollah a terrorist organization.
According to the Congressional Research Service, between 5,000 and 10,000 Iraqi Shiites are fighting for the Syrian government. There are other Shia fighters and some suggest that the Iran provides training for some of these groups.