Arab nations have called on Syrian President Bashar al-Assad to swiftly give up power as his troops launched a fresh assault on rebels in Damascus and the second city Aleppo.
Oil prices hit two-month highs this week, driven by Federal Reserve stimulus hopes and Middle East unrest, while soyabeans soared to a record high as US supplies were hit by drought.
Rebels seized control of Syria's border crossings with Iraq on the bloodiest day of the uprising against President Bashar al-Assad, as China and Russia dismayed the West by blocking UN action against his regime.
Canada issued a scathing retort on Thursday after Russia and China vetoed another UN resolution to pressure the Syrian regime to rein in its crackdown on a 16-month-old rebellion.
UN chief Ban Ki-moon and international envoy Kofi Annan called on the UN Security Council to take strong action on the Syria conflict ahead of a vote Thursday on a western-backed resolution calling for sanctions.
Rebels declared the battle to "liberate" Damascus has begun as heavy fighting raged across the city on Tuesday and Russia said an agreement is possible for a UN resolution on the Syria crisis.
Syria's army blasted rebel strongholds in Damascus with mortars Sunday, sparking the "most intense" fighting in the capital since the revolt erupted 16 months ago.
Syrian troops with tanks and helicopters slaughtered more than 150 people in a central village, rights activists said on Friday, prompting the opposition to call for urgent UN intervention.
Russia will host a top opponent of Syrian President Bashar al-Assad on Wednesday hoping to find common ground with one of the most scathing critics of its refusal to turn against the Damascus regime.
International envoy Kofi Annan has arrived in Syria after admitting that his peace plan has so far failed to end nearly 16 months of carnage, as scores more die in the violence-wracked country.
Russia accused the West on Tuesday of seeking to distort an agreement for a political transition in Syria, after international peace envoy Kofi Annan said a ceasefire was imperative.
Exiled opposition groups tried to forge a common vision for a transition in Syria as they met Monday in Cairo as the UN rights chief accused both the regime and opposition of "serious" violations.
The opposition and state media on Sunday both branded an international plan for a transition in strife-torn Syria a failure, as the death toll for a weekend of violence topped 160.