Here's the latest summary of today's events:

• The US has condemned Russia and China's veto of a new draft resolution on Syria as "highly regrettable". The UK and France were also highly critical of the countries' third veto, with the French UN ambassador accusing Russia and China of buying time "for the Syrian regime to smash the opposition".

• Russia's ambassador accused western countries of "attempting to fan the flames of conflict". Vitaly Churkin said the draft resolution vetoed by Russia and China was "biased", with threats of sanctions "levelled exclusively at the government of Syria. China's ambassador said the resolution would have "further aggravated the turmoil".

• In Syria there have been further clashes between government troops and rebel fighters. In Damascus three government tanks are reported to have been destroyed by anti-government fighters, while gunfire was heard in neighbourhoods to the east of the city. Rebels are reported to have seized at least two major border crossings, into Turkey and Iraq.

• Photos and video emerged of Syria's embattled ruler, Bashar al-Assad on Thursday, reportedly swearing in his new defense minister. Assad's whereabouts remain unclear, with varying rumours placing him in the Syrian port of Lattakia, the presidential palace in Damascus and elsewhere. Assad had not been seen since the blast which killed three members of his inner circle on Wednesday.

• US presidential hopeful Mitt Romney used the crisis in Syria to attack Barack Obama on Thursday afternoon, saying the president had "abdicated leadership". "While Russia and Iran have rushed to support Bashar al-Assad and thousands have been slaughtered, President Obama has abdicated leadership and subcontracted US policy to Kofi Annan and the United Nations," Romney said.

• After the draft resolution was vetoed by Russia and China the UK tabled a new proposal which would extend the stay of a UN observer mission in Syria. The proposal will be voted on at the UN in New York on Friday and would see the mission stay for up to another 30 days. The vote looked unlikely to pass on Thursday, however, after the White House said it did not support extending the mission.

Mitt Romney has waded into the diplomatic row over Syria, blaming President Barack Obama for a "lack of leadership" on the crisis.

Romney accused Obama of abdicating the US role to the United Nations in an attack on Thursday. "While Russia and Iran have rushed to support Bashar al-Assad and thousands have been slaughtered, President Obama has abdicated leadership and subcontracted US policy to Kofi Annan and the United Nations," Romney said in a statement.

The Associated Press is running some quotes from an interview with a woman in the Muhajereen neighbourhood of Damascus.

"It is a war going on here, literally a war," said the 25-year-old, who spoke to AP on the condition of anonymity due to safety concerns. The sounds of battle had kept her up all night and she stayed home from work because she feared random gunfire, she added.

"It reminded me of that night when the Americans shelled Baghdad nine years ago," she said. "I was watching it on TV, but today I'm living a very similar situation."

RT reporter Maria Finoshina has been tweeting some pictures taken today on a drive around Damascus. Some of them provide a different perspective on the city from the stories of tanks and RPGs that we've mostly heard today.

A couple of interesting snippets from Al Jazeera's Syria live blog – quoting the Revolution Leadership Council of Damascus they report that "tension is mounting" in the city.

Tension is overwhelming in Damascus amidst hearing the sounds of gunfire and blasts everywhere and seeing helicopters in: Mazzeh, Barzeh, Kafar Sousseh, Rukn Eddin, Sina'a, Midan, al-Hajar al-Asswad, and Bab Sreijeh. At dawn, there was a power cut in: Mazzeh, Kafar Sousseh, Barzeh and Qaboun.

There are also reports that Syrian rebel fighters seized control of "all border crossings between Iraq and Syria" on Thursday. "All the border points between Iraq and Syria are under the control of the Free Syrian Army," Adnan al-Assadi, Baghdad's deputy interior minister, told AFP by telephone.

An update on the whereabouts of Syrian president Bashar al-Assad: he is reportedly in the presidential palace in Damascus, but no one is 100% sure. Syrian state television showed video footage today of Assad in a meeting with the new defense minister, Fahd al-Freij, at the palace, but some are sceptical as to when it was filmed. Here's a photo from the purported meeting.

AFP quoted a source as saying Assad was in the presidential palace in Damascus, while there are some rumours that the president fled to the Syrian port of Lattakia, although no one really believes that.

The journalist Nabil Abi Saab, who works out of the UN headquarters here in New York, has uploaded that UK draft resolution to his blog. Here are the terms:

1. Decides to renew the mandate of the United Nations Supervision Mission in Syria (UNSMIS) for a final period of 30 days, taking into consideration the Secretary-General's recommendations to reconfigure the Mission, and taking into consideration the operational implications of the increasingly dangerous security situation in Syria;

2. Expresses its willingness to renew the mandate of UNSMIS thereafter only in the event that the Secretary-General reports and the Security Council confirms the full implementation of paragraph 2 of resolution 2043 and a reduction in the level of violence sufficient to allow UNSMIS to implement its mandate;

3. Requests the Secretary-General to report to the Council on the implementation of this resolution within 15 days;

4. Decides to remain seized of the matter.

Here's the Guardian's full news story on events at the UN this morning, featuring more in-depth quotes from the main parties.

After Russia and China vetoed the security resolution proposal, the French ambassador, Gérard Araud declared that "'history will prove [Russia and China] wrong, and it will judge them".

"It is now clear that Russia merely wants to win time for the Syrian regime to smash the opposition," he said.

Russia's ambassador, Vitaly Churkin, fought back against the criticism, saying countries had "attempted to fan the flames of conflict within the UN Security Council". "The draft which was just voted on was biased. The threats of sanctions were levelled exclusively at the government of Syria. This runs counter to the spirit of the Geneva document and does not reflect the realities in the country today." China also believed the resolution to be "seriously problematic, with uneven content that is intended to put pressure on only one party". The country's ambassador Li Baodong said countries had made "unfounded accusations against China", adding that the resolution would "not only further aggravate the turmoil, but also result in spill over to other countries in the region". However Susan Rice, the US ambassador, said that the suggestion that the resolution would give the green light for foreign forces to enter Syria was "paranoid if not disingenuous". "It would in no way authorise or even pave the way for foreign military intervention," Rice said. She said the resolution "would not even impose sanctions at these stage".

This video purports to show the scene at Bab al-Hawa, the main Syria-Turkey border crossing which rebels are said to have captured earlier today.

Reports suggest that Syrian rebel fighters captured buildings at the border crossing earlier on Thursday. Rebels have tried to seize the Bab al-Hawa gateway – a vital commercial crossing – several times in the last 10 days, succeeding after a confrontation with Assad soldiers.

In the video one of the rebels uses a long pole to deface a posted of Bashar al-Assad, the embattled Syrian president.

About 20,000 Syrians have travelled across the main Syrian border crossing into Lebanon over the past 24 hours, a Lebanese security source has told Reuters.

Around 5,000 Syrians make the crossing on a usual day, representing a four-fold increase. Non-Syrians, including diplomats and international aid workers, have apparently also made the crossing. From Reuters:

Lebanese minister of social affairs Wael Abu Faour did not comment on the total number of Syrians who had crossed but said that 8,500 Syrian refugees from Damascus made the trip in the last 24 hours. Abu Faour told journalists that the Lebanese government would open school buildings for refugees to live in and had received offers of help from Arab countries. The Lebanese security source said foreigners including diplomats and some international aid workers were among those who crossed the border on Thursday.

Here's the full statement from Britain's foreign secretary William Hague on the veto this morning, accusing Russia and China of having "turned their back on the people of Syria in their darkest hour".

This course of action was necessary and reasonable and it was called for by the Arab League, by special envoy Kofi Annan, supported by countries across the council, like India, Morocco and Columbia. It was not a Western proposition. It was what people in governments all over the world wanted to see, and there was nothing in it that would have authorised military action. So the decision by Russia and China, in the view of the United Kingdom, to veto this resolution is inexcusable and indefensible. When it came to the time to turn agreements, which they have supported, into action to end the violence, they stood aside from that. They have turned their back on the people of Syria in their darkest hour.

The White House says it does not support extending the UN observer mission in Syria, criticising Russia and China's vetos as "highly regrettable" and "highly unfortunate".

"They are on the wrong side of the Syrian people, the wrong side of hope for peace and stability in the region," White House spokesman Jay Carney told reporters after the vetoes were cast in New York. "It was a highly regrettable decision."

Britain has drafted a new resolution to extend the mission in Syria "for a final period of 30 days", and it could be voted on later today, however the likelihood of that extension now looks less certain.

Reuters reported that Carney, who was aboard Air Force One with President Obama on the way to Florida, said Washington had made clear to the Assad regime that it would be "held accountable" if it uses chemical weapons against the opposition.

Government troops have stormed a Damascus district with tanks for the first time, according to a UK-based rights group.

"The army stormed the Qaboon district with a large number of tanks," Al Jazeera reported Rami Abdel Rahman, of the Syrian Observatory for Human Rights as saying on Thursday.

"This is the first time that tanks enter a Damascus district," Rahman said. Al Jazeera said that the army's move stoked fears of an imminent massacre in the western quarter of the capital, scene of clashes over the past five days.

Earlier the Guardian heard that rebel forces were beginning to take control of parts of Damascus, with one activist based in the eastern Mezze neighbourhood telling my colleague Matthew Weaver that rebels had destroyed three tanks.

They were destroyed using RPGs he claimed. One of the tanks was near the Sham central mound close to a security building, another was on Kafr Souseh square, he said. The FSA do not control tanks, but they did seize an armed vehicle, he said.

International mediator Kofi Annan has voiced his disappointment at the failure of world powers to reach a common position on Syria, Reuters reports.

"The Joint Special Envoy for Syria, Kofi Annan, is disappointed that at this critical stage the UN Security Council could not unite and take the strong and concerted action he had urged and hoped for," his spokesman Ahmad Fawzi said in a statement from Geneva. "He believes that the voice of the Council is much more powerful when its Members act as one."

Good afternoon. Russia and China have voted against the UN security council's draft resolution to impose sanctions on Syria, prompting fierce attacks from the UK, the US and France, who accused Russia of buying time "for the Syrian regime to smash the opposition".

The vote had been postponed to Thursday morning at the UN in New York after a bomb blast in Damascus on Wednesday killed three members of Assad's inner circle: Dawoud Rajha, the defence minister; Asef Shawkat, the assistant vice-president; and Hassan Turkmani, the crisis management chief.

Both Russia and China have consistently resisted the council's attempts to introduce sanctions, meaning their veto was no surprise, but the strength of the response from those in favour gave some indication of the frustrations behind the scenes.

Here's a summary of the day so far from my colleagues Matthew Weaver and Brian Whitaker:

• In the UN security council, Russia and China have vetoed a resolution to impose sanctions on Syria, prompting fierce attacks from the UK and France, who accused Russia of buying time "for the Syrian regime to smash the opposition".

• Amid speculation of President Assad's whereabouts, pictures have now been issued that show him swearing-in the new defence minister. The location appears to be the palace in Damascus.

• Rebel forces are beginning to take control of parts of Damascus as law and order breaks down in the city, an activist based in the eastern Mezze neighbourhood told the Guardian.

• The Syrian government news agency says Qatar is making models of Syrian cities in order to create fake videos (see 12.43pm). State television has also warned that men in Republican Guard uniforms may be rebels in disguise.