The result leaves the Hammers in the Premier League dropzone, third from bottom.
Nuno said afterwards: "We lost the game against a good team. They were better and stronger than us. At half-time we made some changes, we slightly improved but not enough to change the game.
"It is not good going to the international break with this feeling. It is realising that we must do better. We have a lot of work to do. We didn't play good, we have to react, do things better and we are in the fight. It is a moment to reflect and realise we have to do much better. I think the fans today felt disappointed with us and that is what hurts the most."
He also said: "It was not a good performance. In the first half we were never comfortable, we were not able to run, press and lost a lot of duels. I never felt the team was in the right place.
"Slight improvement in the second half but overall we lost against a good team that was better than us.
"In recent weeks we have been really good but I never felt the team was comfortable. We are wishing our players return from international duty healthy and we go again."