Most French airports including international hubs Charles de Gaulle and Orly will stay closed until Tuesday morning due to the volcanic ash cloud covering Europe, France's prime minister said Sunday. Francois Fillon said after a government meeting that all airports north of a line between Bordeaux in the southwest and Nice on the south coast would stay closed at least until Tuesday morning, extending the forecast by a day. 'The weather conditions indicate that the situation will still be difficult for several days,' Fillon told reporters. He added however that Bordeaux and Nice airports and others to the south of the line, including the cities of Biarritz, Toulouse, Marseille and Montpellier, were operating normally. 'We are going to profit from this situation to re-route a maximum number of flights via these airports, which will allow us to bring home the greatest possible number of our fellow citizens stuck abroad,' he said. National carrier Air France meanwhile carried out flights to test the effects of volcanic ash on its aircraft, as did Dutch airline KLM and Germany's Lufthansa. Like Lufthansa, Air France said after the first of the flights that the test plane showed no sign of ash damage. The airport closures had briefly threatened to ground virtually all commercial flights in France. Four airports on Corsica, about 100 miles (165 kilometres) off France's southern coast, were open but processed no commercial flights because activity on the mainland was halted, airport sources said. France's state weather service said the cloud covered the whole of the mainland and particles of ash hanging in the atmosphere were slow to disperse. 'There is no wind or rain to wash them away,' said Meteo France forecaster Patrick Gallois. Transport Minister Dominique Bussereau estimated about 150,000 French people were stranded abroad by the closures. Foreign Minister Bernard Kouchner said France's consulates abroad were mobilised to help them. 'A coordinated European response is needed, and that is not easy,' he told reporters. The airport closures also prevented President Nicolas Sarkozy from going to Poland for the funeral of President Lech Kaczynski on Sunday. 