The blasts come amid rising tension in Lebanon
resulting from Syria's
civil war, which has sharply polarized the country along sectarian lines and between supporters and opponents of the regime of President Bashar Assad.
Tripoli has previously seen clashes between Sunnis and Alawites, a Shiite offshoot sect to which Assad belongs.
Watch the moment of the blast inside a mosque
Local media showed a column of thick, gray smoke rising over the city and said the explosion caused extensive destruction.
Scene of the blast (Photo: Reuters)
Outside the mosque (Photo: Reuters)
The officials said the blasts went off near mosques in the overwhelmingly Sunni city on Friday, the Muslim day of prayer, when places of worship would be packed. They said there were casualties but did not give a number.
The officials spoke on condition of anonymity in line with regulations.
One of the blasts exploded outside the Taqwa mosque, where Sheik Salem Rafei, a Salafi cleric opposed to Lebanon's militant Shiite Hezbollah
group, usually prays. It was not clear whether he was inside.
The second went off about five minutes later in the Mina district of Tripoli, but no details were immediately available.
Attacks have become common in the past few months against Shiite strongholds in Lebanon, particularly following Hezbollah's open participation in Syria's civil war.
But attacks against Sunni strongholds have been rare. So far, no group claimed responsibility for the attacks.