Sterling fell and the Swiss franc rose to a one-week high against the dollar on Thursday after British police said they had thwarted a plot to blow up aircraft in mid-flight. The dollar was under pressure ahead of U.S. June trade data at 1230 GMT. After the Federal Reserve paused in its 2-year-old tightening cycle this week, some analysts expected market focus to shift to U.S. imbalances. Sterling slid in jittery trade from a 15-month high above $1.91 hit earlier this week after British police arrested 21 people and as short-haul flights to and from London's Heathrow airport were cancelled. Britain raised its security threat to "critical" after police said they had foiled a plot to blow up aircraft in mid-flight between Britain and the United States. The U.S. raised the threat level for commercial flights originating in the United Kingdom to "red" or severe. Analysts said the Swiss franc and yen were seeing safe-haven flows as they had strong external positions and tended to gain when capital was repatriated. "Markets are trading nervously in response to the upgrading of the terror threat on both sides of the Atlantic, and that's unlikely to go away for the rest of today," said Steven Pearson, chief currency strategist at HBOS Treasury Services. By 1124 GMT, sterling was 0.1 percent weaker on the day at $1.9022 , some 60 ticks below session highs. It hit a one-week low against the euro at 67.70 pence , and also against a basket of currencies at 102.8. The euro was steady at $1.2855 , while the dollar lost 0.44 percent to 114.78 yen . The single currency was also down around half a percent against the yen, tracking back from a record high hit in Asian trade at 148.60 yen according to Reuters data . The dollar was steady against the Swiss franc at 1.2246 francs, recovering from an earlier one-week low of 1.2195 francs. "I think that the market is already a bit calmer now and in a way ready to look towards the U.S. trade data," said Niels Christensen, senior currency strategist at Societe Generale in Paris.