Syria's army unleashed a barrage of rocket and artillery fire on rebel-held areas in a central province today as part of a widening offensive against fighters seeking to oust President Bashar Assad.
At least 80 people were killed in fighting nationwide, according to activist groups.
The United Nations said a record number of Syrians streamed into Jordan this month, doubling the population of the kingdom's already-cramped refugee camp to 65,000. More than 30,000 people arrived in Zaatari in January - 6,000 in the past two days alone, the UN said.
The newcomers are mostly families, women, children and elderly who fled from southern Syria, said Melissa Fleming, spokeswoman for the United Nations High Commissioner for Refugees.
She said the UNHCR was working with the Jordanian government to open a second major camp nearby by the end of this month.
Many of the new arrivals in Zaatari are from the southern town of Daraa, where the uprising against Mr Assad first erupted nearly two years ago, the Britain-based charity Save The Children said today.
Five buses, crammed with "frightened and exhausted people who fled with what little they could carry", pull up every hour at the camp, said Saba al-Mobasat, an aid worker with Save The Children.
The exodus reflected the latest spike in violence in Syria's civil war. The conflict began in March 2011 after a peaceful uprising against Mr Assad, inspired by the Arab Spring wave of revolutions that toppled leaders in Tunisia, Egypt, Libya and Yemen, turned violent.
Activists said the army recently brought in military reinforcements to the central province of Homs and launched a renewed offensive aimed at retaking patches of territory that have been held by rebels for months.
An amateur video posted online by activists showed rockets slamming into buildings in the rebel-held town of Rastan, just north of the provincial capital, Homs. Heavy gunfire could be heard in the background.
Another video showed thick black and grey smoke rising from a building in the besieged city. "The city of Homs is burning... day and night, the shelling of Homs doesn't stop," the narrator is heard saying.
Troops also battled rebels around the capital, Damascus, in an effort to dislodge opposition fighters who have set up enclaves in surrounding towns and villages.
The troops fired artillery shells at several districts today, including Zabadani and Daraya, according to the Britain-based Syrian Observatory for Human Rights.
Another activist group, the Local Co-ordination Committees, said regime warplanes carried out air strikes on the suburb of Douma, the largest patch of rebel-held ground near Damascus.
The Observatory, which like the LCC relies on a network of activists around Syria, said at least 80 people were killed in violence across the country today, including 11 in Homs.
Other video showed devastation in the Damascus neighbourhood of Arbeen, following what activists said were two air strikes there. A bleeding, wounded man could be seen being helped out of the rubble of the destroyed building. The videos appeared consistent with Associated Press reporting on the fighting.
Last month, the UNHCR said it needed 1 billion US dollars to aid Syrians in the Middle East, and that half of that money was required to help refugees in Jordan.
The agency said 597,240 refugees have registered or are awaiting registration with the UNHCR in Turkey, Lebanon, Jordan, Iraq and Egypt. Some countries have higher estimates, noting many Syrians have found accommodations without registering, relying on their own resources and savings.
In a rare gesture, Syria's Interior Ministry called on those who fled the country during the civil war to return, including regime opponents. It said the government will help hundreds of thousands of citizens return whether they left "legally or illegally".
Syrian opposition figures abroad who want to take part in reconciliation talks will also be allowed back, according to a ministry statement carried late yesterday by the state Sana news agency.
If they "have the desire to participate in the national dialogue, they would be allowed to enter Syria", it said.
The proposed talks are part of Mr Assad's initiative to end the conflict that started as peaceful protests in March 2011 but turned into a civil war. Tens of thousands of activists, their family members and opposition supporters remain jailed by the regime, according to international activist groups.
Opposition leaders repeatedly have rejected any talks that include the president, insisting he must step down. The international community backs that demand, but Mr Assad has clung to power, vowing to crush the armed opposition.
More than 60,000 people have been killed since the conflict began, according to the UN.
Activists also said two cars packed with explosives blew up near a military intelligence building in the Syrian-controlled part of the Golan Heights, killing eight. Most of the dead were members of the Syrian military, the Observatory said.
The Syrian government had no comment on the attacks, which happened in the town of Quneitra last night, and nobody claimed responsibility for them.
Car bombs and suicide attacks targeting Syrian troops and government institutions have been the hallmark of Islamic militants fighting in Syria alongside rebels trying to topple Assad.
Quneitra is on the ceasefire line between Syria and Israel, which controls most of the Golan Heights after capturing the strategic territory from Syria in the 1967 war.