text: The players, who each represent one of the four Welsh regions, have 160 Wales caps between them.
  Dual contracts are funded 60% by the Welsh Rugby Union and 40% by the regions.
  "Having our best players in Wales is vital to the future health of our game," the WRU's Martyn Phillips said.
  The WRU chief executive continued: "Seeing international players re-sign these contracts highlights the success of the programme as we continue to work hard to drive the game forward.
  "We have made no secret of that and the importance both on and off the field at regional and national level in Welsh players playing their rugby in Wales."
  The quartet have made more than 370 regional appearances between them.
  Cardiff Blues' Wales captain Warburton, 28, was the first Welsh player to be given a dual contract in September 2014.
  Flanker Lydiate returned to Welsh rugby on a national dual contract in December 2014 when he joined Ospreys following a spell in France with Racing Metro.
  Scarlets prop Lee, who has won 26 caps for Wales, signed his first dual contract in January 2015.
  Newport Gwent Dragons' Amos, 22, signed his national dual contract in December 2014 and has won 10 caps for Wales.
  Amos' deal is a boost to the Dragons as he had been linked with a move away from Rodney Parade.
  Newport Gwent Dragons head coach Kingsley Jones said: "It's great news for both our region and Wales that Hallam has committed to the Dragons for another two years."
  Cardiff Blues head coach Danny Wilson on Sam Warburton: "With his leadership ability and having achieved so much in the game he's a great asset for Cardiff Blues.
  "It's great that he sees his future here and he will be a key figure for us moving forward."
  Ospreys head coach, Steve Tandy on Dan Lydiate: "With Dan's outlook on the game and his desire to keep learning, even as a senior Wales international and a Lion, he is an example to everybody.
  "I believe he's really grown as an individual and a player since he came to us less than two years ago, and there is still more growth in him, on and off the field."
  Scarlets head coach, Wayne Pivac on Samson Lee: "We're delighted to see another homegrown player committing his future to the club.
  "It's great news that Samson has extended his contract and will continue to ply his trade here at the Scarlets."
  Newport Gwent Dragons head coach Kingsley Jones on Hallam Amos: "He is pivotal to our plans going forward.
  "Not only is he a top class international player he is a quality person and at the age of just 21 is respected by the whole squad and staff."
target: Wales internationals Sam Warburton, Dan Lydiate, Samson Lee and Hallam Amos have signed extensions to their national dual contracts.