"Al-Jazeera presenters have been the targets of a campaign of threats, with in some cases their own safety and that of family members being threatened," the Doha-based channel said in a statement.
The campaign "is aimed at influencing Al-Jazeera's coverage of the uprisings and protests that have swept many Arab countries," it said. "Al-Jazeera now knows the source of these threats which convey nothing but the moral bankruptcy of those behind them," it added.
The statement did not name the source, but did say it was planning to take legal action. However, a source at the broadcaster said the threats emanated from Syria, which has been rocked by protests calling for the ouster of President Bashar al-Assad since mid-March.
Al-Jazeera journalist Dorothy Parvaz, an American of Iranian origin, was jailed in Syria in May for three days before being sent to Iran and then freed. Syrian authorities have sealed off the country to most international media as they crack down on coverage of anti-Assad protests.
The authorities there accuse Al-Jazeera and other international satellite channels of exaggerating the protests and of broadcasting footage without verifying their authenticity.
Because few foreign journalists gain entry to Syria, international media rely heavily on video footage filmed and released by the protesters themselves on Internet sites such as YouTube.
Rights groups say that security forces have killed more than 1,300 civilians and arrested at least 12,000 since the anti-government protests began.
The pan-Arab satellite television channel has been in hot water with several autocratic Arab regimes over its coverage of uprisings sweeping the region since January.
During the protests in Egypt that toppled president Hosni Mubarak, the channel was banned from operating inside the country and nine of its journalists were briefly detained.
In Libya, Al-Jazeera cameraman Ali Hassan al-Jaber was killed on March 12 in an ambush near Benghazi which the rebels blamed on Moamer Kadhafi's forces, and several Al-Jazeera journalists have also been arrested covering the revolt.