Diplomats at the United Nations Security Council are facing a showdown over two competing resolutions on Syria, including one that leaves the door open to military intervention.

A draft resolution by Britain, France, Germany and the United States falls under Chapter 7 of the U.N. charter. It would renew the U.N. observer mission for 45 days and threaten Syria with sanctions if it does not stop using heavy weapons against rebels and civilians. Chapter 7 also would allow for military intervention.

A Russian resolution would renew the mission for 90 days with no threat of sanctions. Russia's U.N. representative promises to veto the Western resolution when it comes up for a vote Wednesday.

Britain's U.N. Ambassador Mark Lyall says Russia and China object to Chapter 7, but he says they have not given any convincing reasons for their objection.

Russian Foreign Minister Sergei Lavrov is accusing the West of 'blackmailing” Moscow into backing a stronger U.N. resolution against Syria.

In Syria Monday, government forces battled rebels in Damascus in what witnesses call the fiercest fighting so far in the Syrian capital.

One Syrian rebel fighter told the French News Agency the fighting is the “turning point” in the 17-month uprising against President Bashar al-Assad.