The heads of five U.N. agencies on Wednesday made an impassioned call to both sides in Syria's conflict to allow aid deliveries countrywide, end siege warfare and halt indiscriminate attacks on civilians.

"The war escalates in many areas. The humanitarian situation deteriorates day after day," the leaders of the U.N. humanitarian aid office and its children's, refugee, food and health divisions said in a joint statement.

The head of Syria's main opposition group has asked Saudi Arabia to increase its support for the rebel Free Syrian Army, his advisor said Wednesday.

Saudi Arabia is one of the main backers of the uprising against Syrian President Bashar Assad in a civil war increasingly seen as a proxy battle between it and regional rival Iran, a close ally of the regime.

A communist MP has registered as the first challenger for the Syrian presidency in a June election expected to return incumbent Bashar Assad to power, the parliament speaker said Wednesday.

"We have received information from the higher constitutional court that member of parliament Maher Abdel Hafiz Hajjar has filed his candidacy for the post of president of the Syrian Arab Republic," Mohammad Lahham said, quoted on state television.

A number of rockets landed on Wednesday in the eastern region of the Bekaa as earlier a Syrian warplane raided the outskirts of the northeastern town of Arsal.

One rocket landed between al-Taybeh and Brital regions, reported LBCI television.

The European Union joined international condemnation of Syria's plan to hold a presidential election on June 3, saying Tuesday the vote would lack credibility while the country remains at war.

EU diplomatic chief Catherine Ashton "deeply regrets the official declaration by the Syrian authorities that presidential elections will be held in Syria on June 3," her spokesman said in a statement.

Syria has handed over 86.5 percent of its chemical weapons, the global chemical watchdog said on Tuesday, amid new claims that Damascus may have launched attacks with an industrial chemical earlier this month.

The latest update comes five days before a self-imposed cut-off of April 27, by which Damascus aimed to have its stockpile removed from Syrian soil, ahead of a June 30 deadline to destroy it.

The Red Cross said Tuesday it was "appalled" by escalating violence in Syria's Aleppo and was awaiting government permission to deliver aid to the pre-war commercial hub.

In a statement, the Geneva-based organization did not assign any blame for mounting casualties in Aleppo, but it urged all parties to observe international law.

New claims have emerged that President Bashar Assad's regime may have launched attacks with an industrial chemical earlier this month, despite an international agreement to eliminate Syria's chemical arsenal.

The latest evidence, cited by the United States and France, comes as Syria plans to hold a June 3 presidential poll, which the United Nations and the Arab League condemned as a blow to efforts to end the three-year-old civil war.

The number of Syrian refugees in Turkey has reached "almost one million," Prime Minister Recep Tayyip Erdogan said on Tuesday, while pledging to keep accepting those fleeing the war.

"Are we supposed to ask our brothers not to come, and to die in Syria?" Erdogan said as he addressed his party's lawmakers in parliament.

A German former rapper who joined jihadists fighting in Syria has been killed in a suicide bombing carried out by rival fighters, jihadist sources and a monitor said Tuesday.

Denis Mamadou Cuspert, who rapped under the name Deso Dogg but took on the name Abu Talha al-Almani in Syria, was reported to have been killed in a suicide attack Sunday in an eastern province.