Lithuania's prime minister said Monday that her country has drawn up plans to shut its border crossings with Belarus indefinitely, after flights at the capital's airport were disrupted repeatedly by suspected sightings of balloons used to smuggle cigarettes across the frontier. Lithuania's National Security Commission met after balloon sightings prompted the suspension of air traffic at Vilnius Airport on three successive evenings — Friday, Saturday and Sunday — causing cancellations, diversions and delays. On Friday, the airport at Kaunas, which is farther from the Belarusian border, also was affected.