UN Undersecretary-General for Humanitarian Affairs Valerie Amos says Syria has denied her repeated requests to visit the country.
UN diplomats said Amos went to Beirut to wait for a visa but received no response. Amos had planned "to discuss the humanitarian situation" with Syrian officials.
Meanwhile, Syrian Foreign Minister Walid Muallem on February 29 asked the UN to clarify the objective of a planned visit by former UN Secretary-General Kofi Annan, who has been appointed UN and Arab League envoy on the Syria crisis.
And a Syrian Foreign Ministry spokesman said that his country would help evacuate Western journalists trapped in the city of Homs, which has been the scene of heavy fighting over the last month.
"Syria will not run away from its humanitarian obligations," Jihad Makdissi said.
Homs Attack Intensifies
In Washington, the U.S. State Department has summoned Syria's envoy to express "outrage" over a monthlong attack on an opposition-held neighborhood of Homs.
The summons came as troops loyal to Syrian President Bashar al-Assad reportedly intensified tank, artillery, and rocket barrages on the neighborhood of Baba Amr.
Opposition activists say the attack is the worst on Homs since antigovernment protests began 11 months ago -- with about eight artillery shells landing every minute and government helicopters flying overhead.
Ground troops reportedly were trying to advance into Baba Amr.
The London-based Syrian Observatory for Human Rights said electricity had also been cut to the Homs neighborhoods of Bayadah and Khaldiyeh -- with military redeployments suggesting preparations for an attack on those areas.
With AP, AFP, Reuters, and dpa reporting
With AP, AFP, and dpa reporting