Jordan said it would be unable to host a new wave of Syrian refugees, as troops loyal to Damascus prepare an offensive for the war-torn country's rebel-held south.

"A large number of Syrians we're hosting in terms of financial resources and infrastructure does not allow for the reception of a new wave of asylum seekers," Jumana Ghanimat, minister of state for media affairs, told AFP.

The announcement comes a day after the UK's Labour Party leader Jeremy Corbyn visited a refugee camp in Jordan.

Corbyn toured Zaatari refugee camp and met with UN officials.

During his tour, Corbyn called on the UK to do more to bring an end to the war in Syria and said that London should join forces with the EU for refugee resettlements.

Some 650,000 Syrian refugees have registered with the United Nations in Jordan since fleeing their country's seven-year war, which was sparked by peaceful anti-government protests in 2011.

Amman estimates the actual number is closer to 1.3 million people and says it has spent more than $10bn hosting them.

"Jordan has not and will not abandon its humanitarian role and its commitment to international charters, but it has exceeded its ability to absorb [more refugees]," said Ghanimat, who also serves as a spokeswoman for the government.

"Everyone should cooperate to deal with any new wave of displacement within Syria's borders," she said, adding that Jordan would work with "concerned organisations" to find an arrangement for the displaced inside Syria.

Her comments came as Syrian government forces prepare an offensive to retake the southern provinces of Daraa, Quneitra and parts of Sweida, still mostly held by rebels.

Southern Syria is a strategically vital zone: it borders both Jordan and the Israeli-occupied Golan Heights and also lies close to Damascus.

After taking out rebel strongholds on the edge of the capital earlier this year, President Bashar al-Assad is now turning his attention to the south.

In recent weeks, Syrian government forces have dropped leaflets over Daraa and Quneitra, warning of impending military operations and calling on the rebels to surrender.

"Jordan is in close contact with Washington and Moscow to maintain an agreement to reduce the escalation in southern Syrian," Ghoneim said.

She said the kingdom was "following the current developments in southern Syrian to reach a formula that protects Jordanian interests along the border and the waves of asylum seekers".

The UN on Thursday warned that escalation in Syria's south could have dangerous repercussions for the estimated 750,000 civilians in the rebel-held area.