VIENNA, Aug 21 (Reuters) - Switzerland has postponed a charter flight to Uzbekistan aimed at helping the evacuation effort from neighbouring Afghanistan, its foreign ministry said on Saturday, citing worsening security that has hindered access on the ground to Kabul airport. "The security situation around Kabul airport has worsened significantly in the last hours. A large number of people in front of the airport and sometimes violent confrontations are hindering access to the airport in Kabul," the Federal Department of Foreign Affairs (FDFA) said in a statement. Thousands of foreigners and Afghans working for embassies and international aid groups have been evacuated from Kabul airport since Taliban insurgents entered the capital a week ago. U.S. President Joe Biden said on Friday that about 13,000 people have been evacuated on U.S. military aircraft since Aug. 14. read more Switzerland said on Friday it had organised a charter flight to Uzbekistan to back up the evacuation of people from Afghanistan. read more "Only a small number of people can currently be flown from Kabul to Tashkent. Since there is no need for evacuations from Tashkent at the moment, the FDFA has postponed the charter flight to the capital of Uzbekistan that was scheduled for today," the FDFA said in its statement on Saturday. Germany has also cancelled evacuation flights scheduled for Saturday and other countries are having increasing difficulties in getting their citizens and local employees out of Afghanistan, the ministry said.