Sweden's 200-year-old posture of military neutrality has been eroding amid European integration, and a perceived new threat from Russia has politicians now talking about abandoning it altogether and joining Nato. Swedish forces have been taking part in peacekeeping, military exercises and some Nato-led missions since the 1990s as the country has joined regional and international forces to reduce its vulnerability in a still-volatile region more than two decades after the cold war ended. Fear of a resurgent Russia is rife in the former Soviet republics across the Baltic Sea, and Moscow's air and naval forces have stepped up patrols near and into Baltic states' airspace and maritime zones over the last two years. Since the Kremlin seized and annexed Ukraine's Crimean peninsula in March 2014, public opinion has shifted from broad opposition to Swedish membership in Nato to one in three Swedes now telling pollsters they favour joining. "I think it's the combination of the perceived threat from Russia and a discussion about the armed forces' inability to carry out their tasks which leads to more Swedes being in favour of Swedish Nato membership," Ulf Bjereld, a political science professor at Gothenburg University, told Swedish Radio. After Swedish media gave broad coverage to rising pro-Nato sentiment, Russia's ambassador to Sweden, Viktor Tatarintsev, warned that Moscow might react militarily if Stockholm were to abandon neutrality and join the alliance. "I don't think it will become relevant in the near future, even though there has been a certain swing in public opinion. But if it happens there will be counter measures," Tatarintsev told the Dagens Nyheter newspaper in June. "Putin pointed out that there will be consequences, that Russia will have to resort to a response of the military kind and reorientate our troops and missiles. "The country that joins Nato needs to be aware of the risks it is exposing itself to." This week, the leader of a key opposition political force, the Centre Party, said she would advocate a move toward Nato membership when the party faithful gather for their annual policy conference. "We lack the ability to defend ourselves for a longer period of time. At the same time, Nato is very clear about the fact that Sweden cannot expect military support if we are not full members of the organisation. We can no longer close our eyes to that," party leader Annie Loof wrote in an op-ed published on Tuesday by Svenska Dagbladet . The Moderates - the largest of the four parties in the opp-osition coalition - already support joining Nato, as do the Liberals. The last of the quartet, the Christian Democrats, also plan to revisit the issue at their party conference in October, leader Ebba Busch Thor told the TT news agency. The ruling coalition of Social Democrats and Greens remains opposed to Nato membership. But they have been supportive of closer engagement with the Western defence alliance and joined four other Nordic countries in April in announcing military collaboration. The pact unites Sweden, Denmark, Norway, Iceland and Finland in a common mission to bolster defences against potential threats from Russia.