BEIRUT - Syria's government banned 17 Western diplomats and its helicopter gunships pounded rebels in a coastal province on Tuesday as President Bashar al-Assad defied international pressure to halt the repression of an uprising against his rule. The declaration of diplomats from the United States, Canada, Turkey and several European countries as unwelcome was a retaliation for the expulsion of Syrian envoys from their capitals last week following the massacre of more than 100 civilians by suspected Assad loyalists. On the battlefront, rebels fought with government forces backed by helicopter gunships in the heaviest clashes in coastal Latakia province since the revolt broke out 15 months ago. It was the second day of combat since the rebels declared an end to their commitment to an internationally brokered ceasefire, saying that the government had continued the repression in defiance of United Nations peace observers. Rebel fighters said eight of their comrades were killed, while the pro-opposition Syrian Observatory for Human Rights said 15 to 20 soldiers were killed. Activists also reported heavy fire by government forces on the city of Homs, a focal point of the uprising that endured a bloody siege for weeks earlier this year. The latest developments only emphasized the precarious state of a peace plan brokered by Nobel Peace laureate Kofi Annan, who has shuttled between Damascus and other capitals on behalf of the United Nations and Arab League. Foreign governments are still clinging to the plan as the only option for finding a political solution and preventing a wider and bloodier conflict. But with the failure of the ceasefire and Assad's intransigence, it is all but in tatters. Nevertheless, Russia and China, Assad's principle defenders on the diplomatic front, said on Tuesday that Annan's efforts should not be abandoned. Russian President Vladimir Putin and his Chinese counterpart Hu Jintao, meeting in Beijing, urged international support for the plan despite calls from Arab and Western states for a tougher response to the bloodshed. The two countries, permanent members of the U.N. Security Council with the power to veto resolutions, have stymied efforts by Western powers to condemn or call for the removal of Assad. The United Nations says Assad's forces have killed more than 10,000 people since the uprising against his family's four-decade rule of Syria broke out in March 2011. Assad says he is fighting to save the country from foreign-backed "terrorists" and will carry out his own reform program. The government says more than 2,700 soldiers or security personnel have been killed by opposition forces.