A roadside bomb exploded at dawn Tuesday on the Masnaa main road in the eastern Bekaa valley, without causing casualties, the state-run National News Agency reported.

The 150-gram bomb, which contained nails, was planted on the side of the road at al-Akramiyeh junction.

The U.S. Department of State reiterated on Tuesday to its citizens the travel warning advisory to Lebanon over safety and security concerns.

“In light of recent escalating sectarian clashes within Lebanon and spillover violence from Syria... We urge all U.S. citizens to avoid all travel to Lebanon because of safety and security concerns,” the U.S. Embassy said in a statement.

The United States has expressed grave concern over the latest battles that pitted fighters supporting Salafist cleric Sheikh Ahmed al-Asir against Lebanese soldiers in the southern city of Sidon.

The U.S. “is gravely concerned by the violent clashes in Sidon,” U.S. State Department Acting Deputy Spokesperson Patrick Ventrell said Monday.

U.N. leader Ban Ki-moon on Monday appealed to Lebanon's armed forces to remain loyal to President Michel Suleiman as sectarian tensions fueled by the Syrian conflict mounted.

Ban is following events in Lebanon with "deep concern," said U.N. deputy spokesman Eduardo del Buey after 16 Lebanese troops were killed as they battled followers of a radical Sunni Muslim sheikh for two days.

Former Prime Minister Saad Hariri on Monday stressed that al-Mustaqbal movement “will remain with the army,” saying the military institution did the right thing by confronting Islamist cleric Sheikh Ahmed al-Asir.

“The army offered major sacrifices and we must all embrace it,” Hariri said in an interview on Future TV.

Caretaker Prime Minister Najib Miqati, Premier-designate Tammam Salam and the former prime ministers on Monday condemned "any attack on the army, whichever side it may come from," while demanding the closure of "all security zones."

In a statement issued after a meeting at the Grand Serail, the conferees "stressed their condemnation and rejection of any attack on the army or any security institution, whichever side it may come from, because the army is the shield of the country in the face of disintegration and the undermining of Lebanon's image and independence.”

Palestine’s President Mahmoud Abbas on Sunday stated his rejection of "any interference" in Lebanese affairs.

“We stress the rejection of the Palestinian factions of any interference in Lebanese affairs,” Abbas said in a phone call with President Michel Suleiman.

The Arab League condemned on Monday the attack against the Lebanese army by supporters of Salafist cleric Sheikh Ahmed al-Asir in the southern city of Sidon on Sunday, calling on all Lebanese powers to exert efforts to avert strife.

Arab League chief Nabil al-Arabi warned of the “dangerousness of targeting the army,” demanding that the assailants be arrested and brought to justice.

Hizbullah slammed on Monday the attack against the army by supporters of Salafist cleric Sheikh Ahmed al-Asir in the southern city of Sidon on Sunday.

Its said in a statement: “The army is the guarantor of civil peace in Lebanon and any attack against it is tantamount to an attack against the entire nation.”

Phalange Party MP Sami Gemayel condemned on Monday the clashes in the southern city of Sidon, voicing the party's support for the army's efforts to crackdown on the gunmen.

He said after the party's weekly politburo meeting: “A curfew should be imposed in all the regions that are witnessing tensions.”