Russia and China on Thursday vetoed a UN Security Council resolution threatening sanctions against Syrian President Bashar al-Assad if he did not end the use of heavy weapons against an uprising, drawing sharp criticism from Western powers.

"Frankly speaking, Western countries attempted to push the United Nations to vote for the sanction resolution in order to get the green light for their military intervention," said the People's Daily, mouthpiece of the ruling Communist party.

The paper's comments echoed those of Russia's UN ambassador Vitaly Churkin, who said the resolution aimed to "open the path to the pressure of sanctions and further to external military involvement in Syrian domestic affairs."

It was the third time in nine months that Russia and China wielded their veto power. As two of the five permanent members of the 15-nation council, the two countries can block any UN resolution.

The veto drew swift criticism from other permanent council members.

Britain was "appalled" by the vetos, said the country's UN envoy Mark Lyall Grant, while US President Barack Obama's spokesman Jay Carney said the vetos were "highly regrettable" and called it a "mistake to prop up that regime".

World powers have so far failed to secure international action to halt the conflict in Syria, part of a series of revolts in the Arab world that have seem changes of government in Tunisia, Egypt and Libya.

Analysts say China's intransigence may stem from its discomfort with Western military action after last year's uprising in Libya, which eventually led to the fall of leader Moamer Kadhafi.

China consistently opposed military action in Libya within the 15-member Security Council, but did not use its veto to block the March 2011 resolution authorising the operation, instead abstaining in the vote.

But it believes the West misinterpreted the resolution and went too far.

The Free Syrian Army (FSA) took control of of the Yaribiyah crossing, known in Iraq as Rabiyah, on Saturday evening and raised their flag, while officials added that Syrian refugees had tried to enter Iraq but Baghdad ordered its security forces not to allow them to cross into the country.

"At 5:00 pm (1400 GMT), some gunmen took control of the Yaribiyah crossing and they were informed that the crossing is now in the hands of the Free Syrian Army," said Atheel al-Nujaifi, governor of the Iraqi province of Nineveh, referring to the Rabiyah crossing by its Syrian name.

He told AFP that because the official working hours of the crossing ended at 4:00 pm, Iraqi officials had already closed their side of the border when it was taken over by Syrian rebels.

"But starting tomorrow, only Iraqis will be allowed to enter from Syria to Iraq," he said.

"We don't know the nature of the side that we are dealing with and until then, we have to wait and see, and we will only give permission to Iraqis to cross the border from Syria to Iraq."

Iraqi border guards First Lieutenant Mohammed Khalaf al-Shammari, stationed on the Iraqi side of the crossing, told AFP that rebels "raised the flag of the Free Syrian Army and tore up pictures of (President) Bashar al-Assad."

Shammari said there was little movement on the Syrian side.

Deputy Interior Minister Adnan al-Assadi said Albu Kamal and Rabiyah were under the control of Syrian rebels. He had said on Thursday that all three crossings were under their control.

Albu Kamal is the Syrian name of the crossing known in Iraq as Al-Qaim, which lies 340 kilometres (210 miles) west of Baghdad in Anbar province.

Syrian rebels have held it since Thursday, and despite government forces having heavily shelled it on Friday night, it remained in their control on Saturday.

And at Al-Waleed, along the southern edge of the 600-kilometre (375-mile) border between the two countries, 150 Syrian families tried to cross into Iraq but were not allowed.

"Iraqi authorities did not let them in, because there are official orders to not receive any refugees," Iraqi border police Captain Ziad al-Rawi said.

He added: "There are Iraqi families on the border now from the Syrian side, but they do not have Iraqi passports, they lost them because of the violence and looting that happened there."

"Iraqi authorities cannot let them in because there are orders not to let anyone come in without documents."

Iraq has appealed for its citizens to return home from Syria in the face of worsening violence there, but government spokesman Ali Dabbagh said on Friday that moving Iraqis by land in Syria was "not safe".

Dabbagh estimated on Thursday that around 100,000 to 200,000 Iraqis still remained inside Syria. He said around 1,000 Iraqis had returned to the country by plane from Syria, and a further 1,500 were waiting at Damascus airport.

The FSA on Saturday also tried to overrun the Nassib border post with Jordan but were repulsed by Syrian government troops, a Jordanian security official told AFP.

Along the Turkish border, dozens of Turkish truck drivers accused FSA rebels of having burned and looted their lorries as they captured Syria's Bab al-Hawa post.