US Treasury Secretary Jacob Lew has urged other countries to contribute more to the economic rescue of Ukraine.He told the International Monetary Fund (IMF) that Ukraine's "sizeable financing needs" meant other nations must add to its $1bn (£597m, 720m euros) loan guarantee, BBC reported.The appeal came as Ukraine's interim prime minister offered to devolve more powers to eastern regions.Pro-Russian separatists there are defying the government.Meanwhile, Washington on Friday announced a third round of sanctions against individuals it has linked to Russia's annexation of Crimea.The US Treasury said it had frozen the US-based assets of one former Ukrainian official, a Crimea-based energy firm and six Crimean leaders, including the chairman of the Crimea electoral commission and the mayor of Sevastopol.Immediate steps 'critical'Mr Lew says the US is "bolstering the IMF program through a complementary aid package, which includes a $1bn loan guarantee and additional technical assistance," in a statement to the IMF."It is critical that the international community - multilateral development banks and bilaterals - take immediate steps to also support the IMF program by providing financing support, given the sizeable financing needs," he adds.ANN.Az