In the meantime, a major insurgent-held town in southwestern Syria has accepted the return of regime leader Bashar al Assad's rule, pro-regime media and a war monitor said on Sunday, though some local activists and rebels disputed a deal had been completed.
Talks in Syria between opposition forces and Russian regime allies broke down Wednesday with no further sessions having been set, according to rebel spokesperson Ibrahim Jabbawi.
Numerous towns in the southwest had already struck their own surrender deals with the government in the teeth of the army advance and aerial bombardment, independently of the main rebel factions.
According to the UN, Jordan hosts about 650,000 registered Syrian refugees and has said that it will not open its border for more to cross.
The explosion rocked an area where arms depots are located in the northern sector of Daraa's northern countryside near the town of Lajat, said the Syrian Observatory for Human Rights, adding that it's not yet clear whether the explosion was a result of a foreign attack or some technical error.
Around 164,000 of the displaced people are now close to the Golan heights - an area of Syria now occupied by Israel - while 60,000 are close to the Jordanian border.
Syrian rebels said Wednesday talks with regime ally Russian Federation over the country's south had collapsed after Moscow threatened a renewed military offensive if they did not agree to tough surrender terms.
Karl Schembri, from the Norwegian Refugee Council, said aid agencies were ready to help if Jordan lets the refugees cross its border.
They "ask the United Nations and the world for protection and global guarantees" for their lives, said opposition official Ali Salhadi.
In a little more than a week the UN's numbers of displaced by the fighting in southern Syria has risen by nearly 100,000 with the United Nations refugee agency warning of a major humanitarian crisis ahead.
The army's offensive follows the capitulation of rebel enclaves near Homs and Damascus, including eastern Ghouta, which was recaptured after a scorched-earth assault that killed over a thousand civilians and laid waste to several towns.
The strategic area was ostensibly protected by a ceasefire agreed by the US, Jordan, and Russian Federation just under a year ago, but President Al Assad is dead-set on retaking it.
Warfare in southwest Syria is sensitive to neighbouring Jordan and Israel.
At the meetings with Russian Federation, rebel negotiators sought a deal for all of Daraa province to come back under government sovereignty, but without the army or police entering the area, an insurgent spokesman said.
But Moscow roundly rejected the terms, the source said.
Jordanian Foreign Minister Ayman Safadi will travel to Moscow on Tuesday to meet with Russia's top diplomat Sergei Lavrov over the crisis, the latest human exodus caused by the more than seven year war.