Let there be no compulsion in religion: Truth stands out clear from error (Surat Al-Baqarah 2:256).
Unto you your religion and unto me my religion (Surat Al-Kafirun 109:6).
There are also many verses in the Quran which suggest otherwise.
Killing is permitted to force people to accept Islam.
Surah 8 : 38. Say to the Unbelievers, if (now) they desist (from Unbelief), their past would be forgiven them; but if they persist, the punishment of those before them is already (a matter of warning for them).
39. And fight them on until there is no more tumult or oppression, and there prevail justice and faith in Allah altogether and everywhere; but if they cease, verily Allah doth see all that they do.
YUSUFALI: Those who believe fight in the cause of Allah, and those who reject Faith Fight in the cause of Evil: So fight ye against the friends of Satan: feeble indeed is the cunning of Satan.
YUSUFALI: Remember thy Lord inspired the angels (with the message): “I am with you: give firmness to the Believers: I will instil terror into the hearts of the Unbelievers: smite ye above their necks and smite all their finger-tips off them.”