Hariri's visit, his first since 2011, comes after open conflict between the army and jihadists on the border with Syria killed 17 troops and left 19 kidnapped.
The former prime minister arrived after announcing earlier that Saudi Arabia, one of his chief allies, had pledged USD 1 billion to shore up the army and security forces against jihadists.
On Wednesday, a day after announcing the funding, Hariri said he would consult with Lebanon's Prime Minister Tammam Salam and the army and security forces on how they would be disbursed.
Fighting that began there on Saturday has eased, with a truce meant to lead to the withdrawal of gunmen from several jihadist groups fighting in Syria and the release of 17 policemen and 19 soldiers thought to be held hostage.
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But the violence is the worst in the border region since the Syrian war began in March 2011, and has raised further concerns about the effects of the conflict on Lebanon.
Despite Beirut's effort to insulate itself from the war next door, the fighting has spilled over and stoked existing political and sectarian tensions in Lebanon.
But many Lebanese Shiites support Assad, and the powerful Shiite Hezbollah movement has sent fighters to bolster his troops against the uprising.
Hariri, 44, has voiced unconditional support for Lebanon's army in the fight against jihadists in Arsal, calling it a "red line".
But some of his constituents accuse the army of allowing Hezbollah free rein to fight in Syria and failing to protect Sunnis.
Today, the situation in Arsal was largely quiet, but an AFP video journalist said several hundred residents who tried return to their homes were forced to flee after coming under sniper fire.
The fighting in Arsal began on Saturday afternoon, when gunmen attacked soldiers after the arrest of a Syrian man accused of belonging to Al-Qaeda's Syrian affiliate Al-Nusra Front.
At least 17 soldiers have been killed, and 19 remain kidnapped along with 17 policemen.
Dozens of militants have been killed, and field hospitals have reported at least 47 deaths, with more than 250 wounded.