American Vice President Joe Biden on Saturday spoke to the premiers of the Czech Republic and Hungary about developments in Ukraine, assuring them of the United States’ commitment to collective defense under NATO’s Article 5, which stipulates that an attack against one member of the alliance is an attack against all. The Czech News Agency reported that Mr Biden spoke for 45 minutes over the phone with Czech Prime Minister Bohuslav Sobotka, discussing new sanctions against Russia for failing to withdraw troops on Ukraine’s border and for failing to de-escalate tension in the area as agreed in talks in Geneva. The two also discussed the situation of OSCE observers - including a Czech national - being held captive by pro-Russian separatists. The Czech Foreign and Defence Ministries are working with partners to try and secure the observers’ release. The Czech Republic joined NATO in 1999; Article 5 was first invoked in 2001 after the 9/11 terrorist attacks against the United States.