NATO foreign ministers are set to discuss Turkey's request for deployment of Patriot missiles to counter a threat from Syria, despite a warning by the Russian president that deployment could increase tensions.
Ivo Daalder, the US ambassador to NATO, said on Monday the ministers’ meeting, which begins on Tuesday in Brussels, was likely to clear the way for the Patriot missiles.
The escalating conflict in Syria is expected to be a major talking point for the alliance's 28 members who share a vow of mutual defence.
Vladimir Putin, the Russian president, said on Monday that any deployment of Patriot missiles would only add to tensions.
"Creating additional capabilities on the border does not defuse the situation but on the contrary exacerbates it," Putin, whose country is not a NATO member, said after talks in Istanbul with Recep Tayyip Erdogan, Turkey’s prime minister.
Both NATO and Turkey insist that the deployment of the US-made surface-to-air Patriot missiles is a purely defensive move.
Al Jazeera's Jonah Hull, reporting from Brussels, said there were high chances of Turkey's request being granted.
"It's extremely likely that the 28 members of NATO ...will agree to come to Turkey's assistance; to meet the request made last month to help augment their air defences in light of a possibility of attack from Syria along and across its 900km border with Syria," he said.
Military sources in Turkey have said NATO is considering the deployment of up to six Patriot batteries and some 300-400 foreign troops to operate them.
The discussion on Turkey's request comes amid a warning by the US president to Syrian President Bashar al-Assad against using chemical weapons on his own people, saying there would be consequences if he were to do so.
Video: US fears over Syria chemical weapons use
"Today I want to make it absolutely clear to Assad and those under his command: The world is watching," Barack Obama said on Monday.
"The use of chemical weapons is and would be totally unacceptable and if you make the tragic mistake of using these weapons there will be consequences and you will be held accountable."
Syrian state media responded by quoting its foreign ministry as saying that it would "never under any circumstances" use such weapons, "if such weapons exist".
Earlier in the day, a senior White House spokesman said that the US and its allied intelligence had monitored Syrian movement of chemical weapons components in recent days.
In another Syria-related development, the UN and European Union announced on Monday that they were scaling back staff and activities from the country.
Martin Nesirky, spokesman for UN chief Ban Ki-moon, said some convoys had been caught in the crossfire between Syrian government and rebel forces, including an incident near the airport in which two staff were injured.
"We can confirm that the UN in Syria will pull out non-essential international personnel with immediate effect," Nesirky said in New York on Monday. "The UN will also suspend its missions within the country until further notice."
The UN said that up to 25 of about 100 foreign staff would leave this week, pointing out that more armoured vehicles were needed after attacks in recent weeks on humanitarian aid convoys and the hijacking of goods or vehicles.