(a) A person is guilty of sexual assault in the first degree when such person (1) compels another person to engage in sexual intercourse by the use of force against such other person or a third person, or by the threat of use of force against such other person or against a third person which reasonably causes such person to fear physical injury to such person or a third person, or (2) engages in sexual intercourse with another person and such other person is under thirteen years of age and the actor is more than two years older than such person, or (3) commits sexual assault in the second degree as provided in section 53a-71 and in the commission of such offense is aided by two or more other persons actually present, or (4) engages in sexual intercourse with another person and such other person is mentally incapacitated to the extent that such other person is unable to consent to such sexual intercourse.
(b) (1) Except as provided in subdivision (2) of this subsection, sexual assault in the first degree is a class B felony for which two years of the sentence imposed may not be suspended or reduced by the court or, if the victim of the offense is under ten years of age, for which ten years of the sentence imposed may not be suspended or reduced by the court.
(2) Sexual assault in the first degree is a class A felony if the offense is a violation of subdivision (1) of subsection (a) of this section and the victim of the offense is under sixteen years of age or the offense is a violation of subdivision (2) of subsection (a) of this section. Any person found guilty under said subdivision (1) or (2) shall be sentenced to a term of imprisonment of which ten years of the sentence imposed may not be suspended or reduced by the court if the victim is under ten years of age or of which five years of the sentence imposed may not be suspended or reduced by the court if the victim is under sixteen years of age.
(3) Any person found guilty under this section shall be sentenced to a term of imprisonment of at least ten years, a portion of which may be suspended, except as provided in subdivisions (1) and (2) of this subsection, or a term of imprisonment and a period of special parole pursuant to subsection (b) of section 53a-28 which together constitute a sentence of at least ten years. Notwithstanding the provisions of subsection (a) of section 53a-29 and except as otherwise provided in this subsection, a court may suspend a portion of a sentence imposed under this subsection and impose a period of supervised probation pursuant to subsection (f) of section 53a-29 .