BEIRUT (Reuters) - Lebanon's army said on Thursday it had foiled planned terrorist attacks by Islamic State on a tourist site and a crowded area, days after suicide bombers killed five people in a Christian village.

Five people involved in the two thwarted attacks, including the mastermind, were arrested on Thursday, an army statement quoted by the National News Agency said.

"Those arrested confessed to having carried out terrorist acts against the army previously. Investigations are continuing," the army said. It gave no further details.

Lebanese security services have been on heightened alert for in recent weeks. Islamic State had urged its followers to launch attacks on "non-believers" during the Muslim holy month of Ramadan, which began in early June.

The government warned this week of a heightened terrorist threat after eight suicide bombers targeted a Christian village on the border with Syria on Monday, killing five people.

Prime Minister Tammam Salam said he feared "a new wave of terrorist operations".

Lebanon has been repeatedly jolted by attacks linked to the war in neighboring Syria, where powerful Lebanese Shi'ite group Hezbollah is fighting in support of President Bashar al-Assad.

A bombing attack in a mostly Shi'ite area of Beirut, claimed by IS, killed more than 40 people in November.

The army said it had arrested more than 400 Syrians in a series of raids in recent days, on suspicion of illegal entry into Lebanon or illegal movement inside the country.

Interior Minister Nohad Machnouk said on Tuesday most of Monday's attackers came from Syria.

(Reporting by John Davison; Editing by Andrew Roche)