An association of Middle Eastern Christians on Tuesday said that two Orthodox bishops reportedly kidnapped by rebels in northern Syria have been released, in a statement citing Syrian sources.

The French "Oeuvre d'Orient" association said that the two -- Bishop Yohanna Ibrahim and Bishop Boulos Yaziji, who were seized on Monday -- were already at Saint Elias cathedral in Aleppo.

An EU plan to buy oil from rebel-held areas of Syria is illegal and an "act of aggression," the Syrian foreign ministry warned on Tuesday in letters to the United Nations.

"In an unprecedented decision that contradicts international law and the U.N. Charter... the European Union has decided to allow member states to import petrol... under the pretext of supporting the opposition," state news agency SANA reported, citing the letters.

NATO must review its ability to fend off threats to the alliance from Syria, including the possible use of chemical weapons, U.S. Secretary of State John Kerry said Tuesday.

"We should ... carefully and collectively consider how NATO is prepared to respond to protect its members from a Syrian threat, including any potential chemical weapons threat," Kerry told a meeting of NATO foreign ministers.

The Russian Orthodox Church on Tuesday called for the release of two Orthodox bishops who Syrian state media said were kidnapped by an armed group in northern Syria.

"We call on the Syrian authorities to do everything possible so that the kidnapped bishops are returned," said the statement, citing Metropolitan Hilarion of Volokolamsk, the chairman of the powerful department of external church relations.

Lebanese Forces leader Samir Geagea condemned on Tuesday Hizbullah's fighting in Syria alongside the Syrian regime, accusing the party of violating the Baabda Declaration that calls for Lebanon to distance itself from regional crises.

He said during a press conference: “The government must hold a session to put an immediate stop to Hizbullah's fighting in Syria.

Caretaker Foreign Minister Adnan Mansour stressed on Tuesday that official memos exchanged between the ministry and international embassies follow strict diplomatic customs and traditions that "he is keen on abiding by", noting that not all letters must be disclosed.

"We receive tens of official memos everyday and the ministry is not obliged to announce anything about them to media outlets,” Mansour said in a meeting with media professionals.

Phalange Party leader Amin Gemayel contacted on Tuesday caretaker Syrian National Coalition leader George Sabra to address the abduction of Syriac Orthodox Archbishop of Aleppo Youhanna Ibrahim and Greek Orthodox Metropolitan of Aleppo and Iskanderun Boulos al-Yaziji in Syria on Monday.

He urged “immediate Arab and international action to save their lives for the sake of the Syrian revolution's reputation.”

The kidnappers of two Orthodox bishops seized in northern Syria are Chechen fighters, sources in the Syriac and Greek Orthodox dioceses in Aleppo said on Tuesday.

"The news which we have received is that an armed group... (of) Chechens stopped the car and kidnapped the two bishops while the driver was killed," an official from the Syriac Orthodox diocese who declined to be named said in a statement posted online.

Former Prime Minister Saad Hariri condemned on Tuesday Hizbullah's fighting in Syria alongside the Syrian regime, warning that it will drag Lebanon towards the strife that President Bashar Assad had “vowed to spread in the region.”

He said in a statement: “Hizbullah's actions in Syria are a crime against Lebanon and the Lebanese and Syria and its people.”

Pope Francis is praying for the liberation of two Orthodox bishops kidnapped by rebels in northern Syria, the Vatican said on Tuesday, a day after Syrian state media reported the abduction.

Francis "is following developments with deep participation and intense prayer for their well-being and liberation," the Vatican's spokesman, Federico Lombardi, told reporters.