US worries deepen as adversaries team up to challenge its dominance

China, Iran, Russia, N. Korea growing ever more defiant even in face of harsh sanctions

For months, the US has warned Iran not to send ballistic missiles to Russia, and told China not to provide military components for Moscow's war in Ukraine.

But Iran is now doing just what Washington said not to, and China is pushing the line. Indeed, the US and its allies are increasingly worried by the speed and intensity with which the three, along with North Korea, are deepening ties to challenge American dominance despite facing some of the most sweeping sanctions the West has ever imposed, according to officials who asked not to be identified discussing matters that are not public.

The defiance fits a pattern of what outside experts - and, increasingly, US and allied officials - see as the growing struggle Washington faces as it seeks to get what it wants around the world.

The examples, they say, are legion.

Venezuela's authoritarian leader brushed aside a months-long US push for free and fair elections, and remains in office after a vote widely seen as rigged. A Washington-led naval coalition has so far failed to lift a Houthi rebel chokehold that's crippled shipping in the Red Sea. Washington and its allies have been pushed out of bases in Africa as China and Russia expand their reach. Beijing has only stepped up its aggression in the South China Sea.

Then there are the allies. Washington finds itself unable to cajole Israel into a ceasefire deal with Hamas.

"US influence is waning, and it's waning rapidly," said Mr Martin Kimani, former Kenyan ambassador to the United Nations and director of New York University's Centre on International Cooperation. "There are rising powers that want to assert themselves more within the multilateral space - from China to others - and the Global South increasingly has a voice."

That's the reality President Joe Biden faces as he joins more than 140 other world leaders in New York for the annual meeting of the United Nations General Assembly.