Vote on Friday will be last chance to elect president and avert political crisis.
The presidency is set aside for a Maronite Christian under a political system that divides the government along sectarian lines.
Outside the church, Christians expressed their fears for the future of the country as the political system remained deadlocked.
“I fear there will not be a president for Lebanon for a long time, we are scared this will effect the Christians here,” one worshipper told Al Jazeera as he left church.
Another said that Lebanon’s leaders needed to make scarifices for the good of the country.
“We are scared for the country, someone has to take control,” she said.
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Siniora dismissed Lahoud’s claims that the country was in a “state of emergency” and said that the government would continue to carry out its duties.
Lebanon’s constitution stipulates that if there is no new president, his powers are automatically transferred to the government – currently led by Siniora.
But Lahoud and the Hezbollah-led opposition have considered Siniora’s government illegitimate since the resignation of all Shia Muslim cabinet members last year.
Parliament has been called to convene again on Friday, a sixth attempt to elect a replacement for Lahoud.
“Come, let’s seize this opportunity,” Sheikh Naim Kassem, deputy leader of the opposition Hezbollah party, said on Sunday.
“If you are serious, we can achieve the election within a week. Otherwise the period will be long,” he said, addressing the ruling coalition.
However, Samir Geagea, a Christian leader in the ruling majority, accused Syrian-backed Hezbollah of obstructing last Friday’s planned election.
“We will not let Syria control again Lebanese politics no matter what happens,” he said at a news conference.
Thousands of Syrian troops were deployed in Lebanon until they were withdrawn in 2005 after 29 years.
The army’s presence had been increased on the streets of the capital Beirut ahead of the scheduled parliamentary session to elect a new president.
Major-General Shawki al-Masri, army chief of staff, visited the Presidential Guards at Baabda Palace on Saturday and said that the army command would strengthen security measures when needed as it “did in the past years”.
The stalemate has prompted fears of a power vacuum or the formation of two rival governments, as was the case at the end of the 1975-1990 civil war.
The ruling coalition, which has 68 deputies in the 127-member parliament, had repeatedly vowed to proceed with a simple majority vote if no agreement is reached.
But Hassan Nasrallah, the Hezbollah leader, said that any attempt by the ruling coalition, which has a slim majority in parliament, would be tantamount to a coup.