Amnesty International urged Jordan on Tuesday not to deny entry to people fleeing the war in Syria, saying families with children have had to wait at the border in recent days.
Since the beginning of the conflict in March 2011, Syrians fleeing the fighting have streamed across the border into Jordan, which says it is hosting some 550,000 refugees.
"The Jordanian authorities must ensure safe access to Jordan for all those wishing to seek safety without discrimination," Said Boumedouha, acting director of the London-based rights group's Middle East and North Africa Programme, said in a statement.
"Persons fleeing Syria should not be denied entry even on a temporary basis as this puts their lives in danger. Jordan has an obligation under international law to ensure that its borders stay open to receive refugees."
According to Amnesty, some refugees and their children have been denied entry to Jordan at the official Nasib border crossing with Syria.
"Jordanian border officials granted them entrance visas but told them that they could not enter Jordan for one month. Their passports were stamped with the message 'return in one month'," the statement said.
For some months, it added, Jordan has not allowed certain categories of people to enter, including Palestinian and Iraqi refugees from Syria as well as people without identity documents or single men.
"This new development of Syrians holding valid passports being turned away may indicate a further hardening of the Jordanian authorities' position," Amnesty said.
"Recent moves by the Jordanian authorities to deny entry to Syrians with correct identity documents signals Jordan's growing weariness to host half a million refugees from Syria, with no end to the crisis in sight."
Jordan has tightened its border fearing a spillover of the Syrian conflict into the kingdom, while officials say the influx has strained the country already limited resources and infrastructure.
Jordanian officials were not immediatly available for comment on Amnesty's statement.
"Regardless of overstretched resources, the Jordanian authorities still have an obligation to ensure that all those fleeing have access to its territory and to safety," said Boumedouha.
"Crucially, the international community must ensure that Jordan and other hosting countries have the financial and technical support they need to provide adequate protection and assistance for the refugees from Syria."
Jordan says it is playing host to some 550,000 refugees from Syria in camps and in urban areas, but the UNHCR said the latest figures were about 600,000.
The influx of so many people is straining the kingdom's already scant resources such as water and energy.