Explosions and gunfire rang out across the Lebanese capital Wednesday as Hizbullah backers trying to enforce a strike against the US-backed government clashed with government supporters and blocked roads. The cause of the explosions was not immediately known, but witnesses and television reports said they may have been rocket-propelled grenades. There was no word on casualties, and the shooting later died down. The strike paralyzed large parts of Beirut. Hizbullah protesters blocked roads with burning tires, dirt, old cars and garbage cans to enforce a labor strike against government economic policies and to demand pay raises. The violence deepened tensions in a country already mired in a 17-month-old political crisis pitting the Iranian- and Syrian-backed Hizbullah against the government of Western-backed Prime Minister Fuad Saniora. The troubles have left Lebanon without a president since November. The strike was called by labor unions after they rejected a last-minute pay raise offer by the government as insufficient. But it turned into a showdown between Hizbullah and the government. The clashes began when government and opposition supporters in the Muslim sector of Beirut exchanged insults then began stoning each other. Witnesses said security forces intervened and gunshots were heard, apparently troops firing in the air to disperse the crowds. A cameraman for Hezbollah's al-Manar television was beaten by a soldier, the station reported. Bystanders wrapped a shirt on his head to stop the bleeding before he left on his motorcycle. A soldier also was hit in the mouth by a stone. Two other news photographers were hurt by, according to witnesses and television reports. Earlier in the same area, a stun grenade thrown into a crowd lightly injured three protesters and two soldiers, the state-run National News Agency said. It was not immediately clear who threw the stun grenade. The disturbances took on a sectarian tone. The clashes spread to several mixed Sunni-Shiite neighborhoods, with Sunnis backing the government and Shiites supporting the opposition. Armed civilians appeared on some streets. Troop reinforcements raced in armored carriers from one neighborhood to another to contain the disturbances. The strike paralyzed Beirut international airport. Airport employees joined for six hours while opposition protesters blocked the roads leading to the country's only air facility. The action led to the cancellation or delay of 19 incoming and 13 outgoing flights. The unrest and roadblocks led labor unions to cancel the main public demonstration planned to coincide with the strike. Lebanon's political crisis took a turn for the worse this week when the government decided to confront the powerful Hezbollah. The Cabinet on Tuesday said it would remove Beirut airport's security chief over alleged ties to Hezbollah. Lebanon's top prosecutor is investigating allegations by pro-government leader Walid Jumblatt that Hizbullah set up cameras near the airport in Hezbollah's stronghold of south Beirut to monitor the movement of anti-Syrian Lebanese politicians and foreign dignitaries. Jumblatt suggested the militant group was planning to bomb aircraft to assassinate senior leaders. The government also declared that a telecommunications network used by Hizbullah for military purposes was illegal and a danger to state security. Hizbullah is listed as a terrorist group by the United States. It has fought Israel for more than two decades, lastly in the 2006 summer war, and enjoys wide support among Lebanon's 1.2 million Shiites who are believed to be the country's largest sect. The political crisis has exacerbated the country's economic problems. Rising oil prices and a weakening US dollar, the favored currency here, have driven up the cost of living. Just as the country is divided politically, the unions were split as well on whether to support the strike. The strike was largely confined to Shiite areas of Beirut and its southern suburbs where support for Hizbullah is strong. It was largely ignored in Sunni and Christian areas of the city which support the government. In areas where government support is strong, some businesses were open but many people stayed off the streets and traffic was lighter than usual amid a heavy army presence. Many schools throughout the city were closed because there was no busing for fear of unrest on the roads. Protesters also blocked highways in opposition strongholds in southern, northern and central areas of the country to prevent motorists from getting to Beirut. The US Embassy advised Americans to avoid areas where protests were going, to take "reasonable" security precautions and maintain a low profile in public.