South Korea\'s parliament Tuesday approved a free trade agreement with the United States, minutes after an opposition legislator had exploded a tear gas canister in the assembly in protest over the pact. Legislators voted 151-7 in favour of the long-delayed deal, live TV footage showed, after ruling party members had caught the opposition off guard by calling a snap parliamentary session. Legislators coughed and wiped their eyes after the canister went off next to the speaker\'s rostrum. The MP who set off the canister was wrestled out of the chamber by security guards as he shouted protests. Proceedings quickly resumed and the sweeping pact -- first approved in 2007 but repeatedly delayed -- was finally ratified. Lawmakers from the ruling Grand National Party (GNP) earlier in the afternoon unexpectedly entered parliament\'s main hall. \"We have decided to push the free trade deal through parliament by voting, as it is almost impossible to reach a compromise with the opposition,\" GNP lawmaker Park Jun-Sun told YTN television by phone. Opposition lawmakers, upon hearing of the call for a full session, rushed towards the main hall and shouted protests at the deputy speaker. Outside parliament, police stopped non-legislators from entering. The GNP had vowed last week to use its majority to push the agreement through parliament, after the opposition rejected a concession from President Lee Myung-Bak. The ruling party had previously been reluctant to ram the bill through and provoke physical clashes, for fear of a voter backlash before next year\'s general and presidential elections. Opposition lawmakers have blocked previous GNP attempts to approve the deal since it sailed through the US Congress last month. Activists, workers and farmers have meanwhile demonstrated in the streets and police have used water cannon to disperse some protests.