Syrian forces shelled rebels in the battle-scarred Aleppo and blasts rocked Damascus on Saturday, as US Secretary of State Hillary Clinton called for the regime's downfall to be speeded up.
State television said two bombs exploded in the heart of the capital, without reporting casualties.
But across the country the renewed violence has killed at least 47 people — 27 civilians, nine soldiers and 11 rebels, the Syrian Observatory for Human Rights said.
The Britain-based monitoring group said that in the city of Aleppo "areas of Salaheddin district came under shelling by Syrian regime forces," who forced the rebels to stage what they termed a "tactical withdrawal" on Thursday.
A rebel commander insisted his fighters were still putting up strong resistance around Salaheddin.
"Fierce fighting has continued without respite for the past 24 hours as the army tries to push us out of the neighbourhood," Abdel Qader Saleh told AFP by telephone.
The Local Coordination Committees, a network of activists on the ground, later reported "intense and indiscriminate bombardment by aircraft flying over Sakhur and Hanano districts" of Aleppo, Syria's commercial capital.
Troops backed by artillery stormed Salaheddin on Wednesday in the first stage of an offensive to recapture areas of the northern city taken by the rebels since July 20.
In the face of the escalating violence, the US top diplomat on a visit to Turkey said the "number one goal" of Washington and Ankara was to hasten the end of President Bashar al-Assad's regime and stop the bloodshed.
"We are continuing to increase pressure from outside," Clinton told a joint press conference in Istanbul after meeting Turkish Foreign Minister Ahmet Davutoglu and Syrian opposition activists.
"Yesterday in Washington we announced sanctions designed to expose and disrupt the links betweenIran, Hezbollah and Syria that prolong the life of the Assad regime."
Washington on Friday announced sanctions against Syrian state oil company Sytrol for trading with Iran, in a bid to starve both Tehran and Damascus of much-needed revenue.
The US Treasury also said it was adding the Lebanese Shiite militant group Hezbollah, which has close ties with Iran and Syria, to a blacklist of organisations targeted under Syria-related sanctions.
Washington already classes Hezbollah a "terrorist organisation" and it is under US sanctions, but Friday's move explicitly ties the group to the violence in Syria, where Assad is attempting to put down a 17-month revolt.
"Our goal number one is to hasten the end of the bloodshed and the Assad regime, that is our strategic goal," Clinton said.
But no end to the bloody conflict is in sight as witnesses Saturday reported gunfire on the densely-populated Baghdad Street in the heart of the Syrian capital.
Elsewhere in Damascus, state television quoted an official as saying that an "armed terrorist group detonated a bomb in the Marjeh district and fired randomly."
Fighting was also reported in Tadamun, where there were "fierce clashes between the Free Syrian Army and the regime forces," said the Local Coordination Committees.
With the unrelenting violence, Arab foreign ministers will hold emergency talks in Saudi Arabia on Sunday to discuss the conflict and a replacement for international mediator Kofi Annan, who resigned in frustration over a failed peace deal.
World powers are expected to name veteran Algerian diplomat Lakhdar Brahimi as the new UN-Arab League envoy for Syria early next week.
In Istanbul, Clinton met with Syrian activists and refugees, who she said were committed to "a free, inclusive and democratic Syria" but need support from the international community to be ready for the eventual fall of the Assad regime.
French President Francois Hollande also Saturday backed "support for the Syrian opposition and the determined search for a political transition in Syria," as well as humanitarian aid.
Clinton also announced an additional US$5.5 million in aid for those fleeing fighting in Syria that monitoring groups say has now claimed over 21,000 lives.
Turkey is currently home to some 55,000 refugees living in camps along the Syrian border, with close to 10,000 seeking safety this week alone.
A French cargo plane carrying tonnes of aid supplies and medical equipment landed on Saturday inJordan for tens of thousands of Syrian refugees from across the border.
In Lebanon, another neighbour where tensions have spilled over, the military prosecutor general accused Syrian security chief General Ali Mamluk and former Lebanese minister Michel Samaha of planning attacks.
A judicial source said they were "suspected of forming a group to provoke sectarian killings and terrorist acts using explosives, which were transported and stored by Michel Samaha."
Their targets, mostly in northern Lebanon near the border, would have been religious and political figures, and the men are accused of attempting to stir sectarian strife and undermine the Lebanese state, the source said.
