Iranian President Mahmoud Ahmadinejad has been welcomed by thousands of Lebanese supporters in a visit that underscores the deep divisions between the Hezbollah militant group and Lebanon's pro-western factions.
Mr Ahmadinejad is making his first state visit to Lebanon at a time when tensions have mounted between Iranian-backed Hezbollah and US-allied parties.
The growing crisis has raised fears over the fate of the fragile unity government that includes both sides and has managed to keep a tenuous calm in the conflict-torn nation.
Hezbollah's opponents in Lebanon often brand it a tool of Tehran and fear the movement - which boasts widespread support among Shiites and has the country's strongest armed force - is seeking to impose control over the country.
Hezbollah and its allies, in turn, said their political rivals are steering Lebanon too far into the American camp. The visit by the leader of Hezbollah's most powerful ally, Iran, throws Lebanon's divisions into sharp relief.
Thousands of Lebanese lined the main highway into the capital from Beirut's airport, where Mr Ahmadinejad arrived.
Many waved Lebanese and Iranian flags, and giant posters of Mr Ahmadinejad towered over the road, while loudspeakers blasted anthems and women in the crowd sold Hezbollah flags and balloons to onlookers.
However, Hezbollah's rivals expressed concern over the message sent by the Iranian leader's visit.
A group of 250 politicians, lawyers and activists sent an open letter to Mr Ahmadinejad on Tuesday, criticising Tehran's backing of Hezbollah and expressing worry that Iran is looking to drag Lebanon into a war with Israel. Iran funds the group to the tune of millions of dollars a year and is believed to provide much of its arsenal.
Mr Ahmadinejad will meet Mr Hariri and Lebanon's president during his visit, which lasts until Friday. But the biggest splash will come from his welcome by Hezbollah. Iran has strong ties to Hezbollah, which in many Shiite areas runs nearly a state-within-a-state.