Supporters of Lebanon's Hezbollah-led opposition blocked main roads in Beirut with burning barricades on Wednesday, paralysing the city and deepening a political conflict with the U.S.-backed government.

The opposition supporters set cars and tyres ablaze to block the main road to Beirut's international airport, where air traffic was suspended because of a strike by staff taking part in a labour union protest to demand higher wages.

The opposition has backed the strike. Activists loyal to Hezbollah, a political group with a guerrilla army and backing from Iran and Syria, also blocked routes to Beirut's main commercial district.

The scenes were reminiscent of an anti-government protest in 2007 that led to some of Lebanon's worst internal strife since its 1975-90 civil war. A stun grenade exploded in Beirut, slightly wounding one person, a security source said.

In Lebanon's deepest political crisis since the civil war, Hezbollah has been leading a campaign against Prime Minister Fouad Siniora's government since November 2006. The standoff has left Lebanon without a president for five months.

Hezbollah, Lebanon's most powerful Shi'ite faction, and its allies in the opposition have deemed Siniora's cabinet illegitimate since all of its Shi'ite Muslim ministers resigned in 2006.

SPYING ACCUSATIONS

Tension between the government and Hezbollah escalated sharply on Tuesday.

The government accused Hezbollah of violating Lebanon's sovereignty by operating its own communications network and installing spy cameras at the airport.

The government, supported by Arab states including Saudi Arabia, also removed the head of Beirut airport security in another challenge to Hezbollah.

The group said the communications network was part of its security apparatus and had played a major role in its war with Israel in 2006.

Hezbollah was the only Lebanese faction allowed to keep its weapons after the civil war to fight Israeli forces occupying the south. Israel withdrew in 2000 and the fate of Hezbollah's weapons is at the heart of the political crisis.

A U.N. Security Council resolution that ended the 2006 war between Hezbollah and Israel bans the group from rearming and rebuilding its military infrastructure in south Lebanon.

Governing coalition leaders allege Hezbollah is spying on the airport to monitor their movements. Eight members of the anti-Syrian coalition have been assassinated since 2005.

Government posts in Lebanon are divided according to a sectarian system. The government is backed by Saad al-Hariri - Lebanon's most powerful Sunni Muslim leader.

The main labour union is calling for higher wages to help offset rises in the cost of food, fuel and other goods. The government increased the minimum wage by two-thirds on Tuesday but unions want more.