DAMASCUS, Syria - A strong explosion rocked the Syrian capital Thursday near a busy market and the country's highest court, wounding at least three people and sending clouds of black smoke into the sky. The blast came as tensions threatened to spread across the region. Neighboring Turkey deployed anti-aircraft guns and other weapons alongside its border with Syria, nearly a week after Syrian forces shot a Turkish military plane out of the sky, Turkish state TV said Thursday. Major world powers will meet Saturday in Geneva for talks on Syria, but few observers expect a major breakthrough. Syria has the protection or Russia, a veto-wielding member of the U.N. Security Council, and has so far been impervious to international pressure. Russian Foreign Minister Sergey Lavrov said Thursday that Moscow will not endorse a call for Assad to give up power. "We are not supporting and will not support any external meddling," he said. External players must not dictate ... to Syrians, but, first of all, must commit to influencing all the sides in Syria to stop the violence. It was not clear who was behind Thursday's blast in Damascus. But rebel fighters are launching increasingly deadly attacks on regime targets, and several massive suicide attacks this year suggest al-Qaida or other extremists are joining the fray. An Associated Press reporter at the scene of the blast said some cars were charred and many had their windshields blown out. "I did not see any wounded people, but cars and nearby shops were damaged," said Fawaz Mishhim, a witness who was in a nearby market when he heard the explosion. Syria's state-run TV said the explosion was in the parking lot of the Palace of Justice, a compound that houses several courts. The blast happened at 1 p.m. near the capital's famous Hamidiyeh Market, an area crowded with families stocking up on food and other supplies for the weekend, which begins on Friday in Syria. Witnesses reported hearing one blast, but state-run TV said two explosions struck the area. The report also said a roadside bomb was found but did not explode. Elsewhere in Syria, activists reported clashes between troops and rebels and said more than a dozen people were killed nationwide. Some of the heaviest battles were in the eastern city of Deir el-Zour, activists said. Activists say more than 14,000 people have been killed since the Syrian uprising began in March 2011. Turkey, a former ally, has become one of the strongest critics of the Assad regime. Tensions between the two countries spiked following the downing of the Turkish plane last week. Syria insists the Turkish military plane violated its air space on Friday. Turkey says the jet had unintentionally strayed into Syria's air space and was inside international airspace when it was brought down over the Mediterranean by Syria. The search for two missing pilots continued in Syrian waters but hopes for their survival are dim, Turkish authorities said. The Turkish military said Thursday that research teams have found some pieces of the plane as well as equipment belonging to the pilots. A small convoy of military trucks towing anti-aircraft guns entered a military outpost in the border village of Guvecci, which faces a Syrian military outpost, according to TRT television footage. Several anti-aircraft guns also have been deployed elsewhere alongside the border. Some trucks were seen carrying self-propelled multiple rocket launchers, the footage showed. Ties between Turkey and Syria have not been so low since the late 1990s, when the two countries almost went to war. Tensions ran high in the 1980s and 1990s as Turkey developed military ties with Israel and Syria sheltered Turkish Kurd guerrilla leader Abdullah Ocalan. Now, Turkey is hosting civilian opposition groups as well as hundreds of army defectors who are affiliated with the rebel Free Syrian Army. Turkish President Abdullah Gul was holding a National Security Council meeting on Thursday, TRT said. The meeting, attended by Cabinet members and the military's top brass, is expected to focus on tensions with Syria.