UNITED NATIONS  — Russia has blocked a U.N. Security Council declaration of alarm over the bloody siege of the Syrian town of al-Qusair by Syrian troops and Hezbollah guerrillas, Security Council diplomats said.

Meanwhile, concern about the deteriorating situation in Syria was heightened as fighting spread into Lebanon's territory and a leading Sunni cleric called for a holy war against the Syrian government. Humanitarian efforts by the Red Cross to address civilians caught in the crossfire are being rebuffed, and in Vatican City Pope Franics lamented the defenseless victims of the violence.

With the U.S. hopeful that peace talks in Geneva would begin shortly, weekend developments brought further concern of how the world's powers might influence the two-year-old civil war that has killed more than 80,000 people.

Britain, president of the 15-nation council, had circulated a draft statement to fellow Security Council members voicing "grave concern about the situation in Qusair, Syria, and in particular the impact on civilians of the ongoing fighting."

Qusair, near the Syrian-Lebanese border, is usually home to an estimated 30,000 people. Fighting for control of the town has raged for two weeks. Rebels trapped in Qusair have pleaded for military help and medical aid for hundreds of people wounded in the onslaught by government forces.

Syria's state-run news agency reported that the government told the UN that the International Committee of the Red Cross also won't be allowed into Qusair until military operations are concluded there.

Security Council statements must be agreed unanimously. Russia blocked the draft text, saying it was "not advisable to speak out as the U.N. Security Council didn't when Qusair was taken by the opposition," a council diplomat said on condition of anonymity.

Another diplomat confirmed the remarks.

Moscow's move to block the statement highlights the deep chasm between Russia and Western nations on how to deal with Syria. Russian diplomats in New York did not respond immediately to a request for comment.

The draft statement, obtained by Reuters, also urged forces loyal to President Bashar al-Assad and rebels trying to oust him "to do their utmost to avoid civilian casualties and for the Syrian Government to exercise its responsibility to protect civilians."

It appealed to Assad's government "to allow immediate, full and unimpeded access to impartial humanitarian actors, including U.N. agencies, to reach civilians trapped in al-Qusair."

Diplomats said Russia told council members that the best way to deal with Syria was through intensive diplomacy. However, one council diplomat noted that Russia continues to sell weapons to Assad's government.

Moscow in turn has accused Western and Gulf Arab governments of providing money, arms and other forms of support to the rebels. It is an allegation Assad's government has also repeatedly made.

Russia and China have opposed efforts in the Security Council to impose sanctions on Assad's government and vetoed three resolutions condemning it.

Moscow and Washington are trying to organize a peace conference in Geneva this month that would involve the government and rebels. There has been wrangling over who should participate in the conference and no date has been set for it.

In the meantime, the conflict threatens to draw more entities into it.

A Lebanese security official said Sunday that Hezbollah fighters and Syrian rebels exchanged fire in a remote area of eastern Lebanon. Hezbollah and Syrian rebels are at odds in the civil war, but rarely have their clashes extended into Lebanese territory.

Leading Sunni Muslim cleric Sheikh Youssef al-Qaradawi on Saturday called for holy war against the Syrian government after fighters in response to Hezbollah support of Assad. Al-Qaradawi is among the prominent Muslim scholars who have been vociferous supporters of the revolutions that have shaken the Arab world in the last two years.

On the humanitarian front, Pope Francis decried the "plague of kidnappings" in Syria as he spoke from his studio window overlooking St. Peter's Square on Sunday.

Both rebels and pro-regime forces have abducted political foes, members of rival sects and others, including journalists, to settle scores or for ransom. Among those snatched were two Orthodox bishops who were abducted in April.