Amman (AFP) - Jordan's army said Tuesday the kingdom's border with Syria would remain closed, even as tens of thousands of Syrians flee a government offensive towards the frontier.

The commander of the kingdom's northern military region, General Khaled al-Massaid, told AFP that authorities feared the presence of "infiltrators among the displaced".

Around 95,000 Syrians have arrived in the border region "as a result of the latest military operations", he said.

Syrian government troops backed by Russian airpower launched an offensive on June 19 to recapture the country's southern Daraa region along the border with Jordan.

"The borders are closed and the army is being very cautious with the displaced, fearing the presence of... infiltrators with weapons and disguised as women," said the general.

The United Nations said Monday the number of Syrians displaced by the onslaught had already exceeded 270,000, with 70,000 people seeking shelter along the border.

Massaid said 86 trucks had crossed the frontier over the past three days to deliver food and drinking water to the displaced.

Jordan's army has been distributing humanitarian aid and providing medical treatment at three points along the border, he said.

Earlier on Tuesday, UN High Commissioner for Human Rights spokeswoman Liz Throssel urged Jordan to open its border to the "thousands of refugees stranded without adequate shelter".

"We urge all parties to the conflict to protect civilians in southwestern Syria, and to protect those attempting to flee," she said.

Jordan said on June 24 that it would be unable to host a new wave of Syrian refugees and that its northern border would remain closed.

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

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